The United States signed a landmark deal with the Taliban on Saturday, laying out a timetable for a full troop withdrawal from Afghanistan within 14 months as it seeks an exit from its longest-ever war.

The agreement is expected to lead to a dialogue between the Taliban and the Kabul government that, if successful, could ultimately see an end to the grinding 18-year conflict.

Taliban fighter-turned-dealmaker Mullah Baradar signed the accord alongside Washington's chief negotiator Zalmay Khalilzad, at a gilded desk in a conference room in a luxury Doha hotel. The pair then shook hands, as people in the room shouted "Allahu Akbar" (God is greatest).

US Secretary of State Mike Pompeo looked on as the two inked the deal, after urging the insurgents to "keep your promises to cut ties with Al-Qaeda".

The US and the Taliban also agreed to swap thousands of prisoners in a "confidence-building measure" as part of a landmark deal on Afghanistan's future signed in Doha. "Up to 5,000 prisoners of the (Taliban)... and 1,000 prisoners of the other side (Afghan forces) will be released by March 10," the deal said.

Dialogue between the Kabul government and the Taliban is due to begin by that date.

On the eve of the signing, President Donald Trump urged the Afghan people to embrace the chance for a new future. "If the Taliban and the government of Afghanistan live up to these commitments, we will have a powerful path forward to end the war in Afghanistan and bring our troops home," he said.

But the position of the Afghan government, which has been excluded from direct US-Taliban talks, remains unclear and the country is gripped by a fresh political crisis amid contested election results. 

- 'Important first step' -

The Doha accord was drafted over a tempestuous year of dialogue marked by the abrupt cancellation of the effort by Trump in September.

The signing comes after a week-long, partial truce that has mostly held across Afghanistan, aimed at building confidence between the warring parties and showing the Taliban can control their forces.

The United States and its allies will withdraw all their forces from Afghanistan within 14 months if the Taliban abide by the terms of the accord. 

After an initial reduction of troops to 8,600 within 135 days of Saturday's signing, the US and its partners "will complete withdrawal of all remaining forces from Afghanistan" within 14 months.

NATO Secretary General Jens Stoltenberg heralded the agreement as a "first step to lasting peace". "The way to peace is long and hard. We have to be prepared for setbacks, spoilers, there is no easy way to peace but this is an important first step," the Norwegian former prime minister told reporters in Kabul.

Since the US-led invasion that ousted the Taliban after the September 11, 2001 attacks, America has spent more than $1 trillion in fighting and rebuilding in Afghanistan.

About 2,400 US soldiers have been killed, along with unknown tens of thousands of Afghan troops, Taliban fighters and Afghan civilians.

Speaking after the Doha ceremony, Pakistan Foreign Minister Shah Mehmood Qureshi said “We are happy that the Afghans have embarked on a path to peace. Pakistan is a stakeholder to that. We have strived for Afghan peace.”

- 'Happy and celebrating' -

The Taliban said they had halted all hostilities Saturday in honour of the agreement. "Since the deal is being signed today, and our people are happy and celebrating it, we have halted all our military operations across the country," Taliban spokesman Zabihullah Mujahid told AFP.

Any insurgent pledge to guarantee Afghanistan is never again used by jihadist movements such as Al-Qaeda and the Islamic State group to plot attacks abroad will be key to the deal's viability.

The Taliban's sheltering of Al-Qaeda was the main reason for the US invasion following the 9/11 attacks. 

The group, which had risen to power in the 1990s in the chaos of civil war, suffered a swift defeat at the hands of the US and its allies. They retreated before re-emerging to lead a deadly insurgency against the US military and the new government in Kabul.

After the NATO combat mission ended in December 2014, the bulk of Western forces withdrew from the country, leaving it in an increasingly precarious position.

While Afghans are eager to see an end to the violence, experts say any prospective peace will depend on the outcome of talks between the Taliban and the Kabul government.

But with President Ashraf Ghani and rival Abdullah Abdullah at loggerheads over contested election results, few expect the pair to present a united front, unlike the Taliban, who would then be in a position to take the upper hand in negotiations.

Addressing the ceremony in Doha on Saturday, US Secretary of State Mike Pompeo called on the Taliban to honour its commitments to sever ties with jihadist groups.

He called on the Taliban to "keep your promises to cut ties with Al-Qaeda."

"I know there will be a temptation to declare victory, but victory for Afghans will only be achieved when they can live in peace and prosper," he said, adding Pompeo said the US "will closely watch the Taliban's compliance with their commitments, and calibrate the pace of our withdrawal to their actions."

"This is how (we) will ensure that Afghanistan never again serves for international terrorists," Pompeo said.

 Action if Taliban break deal: Pentagon chief

The United States "will not hesitate to nullify" its historic deal with the Taliban if the insurgents renege on their security guarantees and commitment to hold talks with the Afghan government, US Defence Secretary Mark Esper said Saturday. On a visit to Kabul, Esper warned that "should the Taliban fail to honour their commitments they will forfeit their chance to sit with fellow Afghans and deliberate on the future of their country."

"Moreover the United States would not hesitate to nullify the agreement," he added.

Mark Esper was in Kabul on Saturday for a joint declaration ceremony with Afghan President Ashraf Ghani.

According to Afghanistan's national security adviser Hamdullah Mohib, the joint US-NATO-Afghan declaration includes an 18-month withdrawal of foreign troops. "But it is conditional on the agreement between the Taliban and the United States. If those conditions are not met, this date will also change," he said.

A senior Afghan politician told CNN Friday that Afghan government is wary about the upcoming deal, which is meant to trigger intra-Afghan dialogue between Afghan stakeholders and the Taliban.

Main points of Afghan peace deal

The agreement signed by US and Taliban negotiators opens the way for direct negotiations between the insurgents and other Afghans, including the country’s government, on a political future after Washington ends its military presence. The negotiations could also result in a ceasefire.

Here are the main points in the agreement, and a look at how events could unfold.

A gradual US troop withdrawal will begin

The United States has agreed to withdraw American troops from Afghanistan in exchange for assurances by the Taliban that it will deny sanctuary to terrorist groups like Al-Qaeda.

Right now, the United States has about 13,000 troops in the country, down from about 100,000 at the peak of the war nearly a decade ago. They are supported by several thousand others from NATO allies.

The two sides have agreed to a gradual, conditions-based withdrawal over 14 months. In the first phase, about 5,000 troops are to leave within 135 days. During the gradual withdrawal, the Taliban and the Afghan government would have to work out a more concrete power-sharing settlement. That timeframe would give the government the cover of American military protection while negotiating.

Taliban pledge to break with Qaeda

The United States invaded Afghanistan because the Taliban government had given safe haven to Al-Qaeda, which conducted Sep 11, 2001, terrorist attacks on the mainland.

Over the years, even as Al-Qaeda has been decimated by years of US military operations, the Taliban refused to publicly disavow the group, which still pledges allegiance to the Taliban’s supreme leader. As part of the deal, the Taliban commit to breaking with Al-Qaeda and other terrorist groups and keeping them from using Afghan territory to stage attacks against the United States and its allies.

The United States and the Taliban are to establish a joint monitoring body in Qatar, where their negotiations have been held, to assess progress on the commitments.

Other issues include the release of prisoners and the lifting of international sanctions and travel bans on Taliban leaders. US officials say all those steps will be implemented gradually, and only if the Taliban meet their commitments.

Complicated talks between Afghans come next

The agreement between the United States and the Taliban unlocks a difficult but crucial next step: negotiations between the Taliban and other Afghans, including the government, over future power-sharing. Those talks are expected to start soon, within 10 days or so.

But the Taliban, who led most of Afghanistan from 1996 to 2001 before they were toppled by the US military invasion, refuse to recognize Afghanistan’s democratic government. The goal of their insurgency has been returning to power and establishing rule based on their view of Islam.

Other major issues, including women’s rights and civil liberties, are also at stake. Many Afghan women have expressed concern that they have been sidelined from the process, and they fear that protections created for them over the past 18 years could be bargained away to the ultraconservative Taliban movement.

Divisions inside Afghanistan will complicate the negotiations. The democratic side has been bitterly divided by a disputed election, with the main challenger declaring he would form his own government after President Ashraf Ghani won a second term in office.

Deal tied to reducing bloodshed immediately

For much of the negotiating process, the American side demanded a ceasefire that could pause the bloodshed, in which dozens are killed daily, and create space for talks over the future of the country. With violence as their main leverage, the Taliban refused that demand in the early stages of the talks, saying they were willing to discuss it only in negotiations with other Afghans once the United States promised to withdraw its troops.

Eventually, the two sides found a compromise: a significant “reduction in violence” that would not be called a ceasefire. The signing of the deal was conditioned on a seven-day test of that violence reduction, which officials said largely worked. Attacks across Afghanistan, which normally would number as many as 50 to 80 on any given day, dropped to below a dozen.

The reduction in violence is expected to continue into the next phase of the process, until the two Afghan sides can agree to a more comprehensive ceasefire.

EU: Deal first step to Afghan peace process

The European Union said Saturday a landmark deal between the US and the Taliban, and a separate US-Afghanistan declaration, are "important first steps towards a comprehensive peace process" in Afghanistan.

The EU's foreign policy chief Josep Borrell said in a statement that "the current opportunity to move towards peace should not be missed" and the bloc expected "Afghan-owned and Afghan-led negotiations to start without delay in an inclusive manner and aiming at a lasting peace".

The Afghan government was not directly involved in the negotiations resulting in Saturday's deal signed in Doha. But US Defence Secretary Mark Esper was in Kabul to make a joint declaration with the government.

Borrell said the EU stood ready to help with an Afghan peace process in which "all political factions, where notably Afghan women and minorities as well as the civil society, are represented in a meaningful manner".

He added: "It is vital that all people of Afghanistan feel represented in the next government and in peace negotiations. This would help address grievances, including in the context of the recent electoral process, and promote reconciliation."