US President Donald Trump on Tuesday renewed his vow to negotiate a troop withdrawal from Afghanistan, saying he had no desire to kill "hundreds of thousands" in unending fighting.

In one of his few foreign-policy points in a highly partisan State of the Union address to Congress, Trump offered his blessing for ongoing negotiations with Taliban militants. "I am not looking to kill hundreds of thousands of people in Afghanistan, many of them totally innocent," Trump told the joint session of Congress.

"It is also not our function to serve other nations as a law enforcement agency. These are war-fighters, the best in the world, and they either want to fight to win or not fight at all," he said. "We are working to finally end America's longest war and bring our troops back home."

Trump has long questioned the wisdom of keeping troops overseas and has described the war in Afghanistan launched after the September 11, 2001 attacks as a drain on blood and treasure. But last year he abruptly said that he had cancelled a previously unannounced summit at the Camp David presidential retreat with the Taliban because of an attack that killed an American.

He later allowed veteran US negotiator Zalmay Khalilzad to resume the talks, which had taken place for months in Qatar. Under a draft deal, the United States will withdraw troops, and the Taliban will promise not to allow extremists to use Afghanistan as a base as well as to open talks with the internationally recognized government in Kabul.

The Taliban have more recently proposed a limited reduction in violence, an easing of position after previously refusing any halt to attacks it sees as leverage.

 - Little foreign focus -

Trump earlier spoke forcefully against Venezuela's leftist leader Nicolas Maduro, inviting his rival Juan Guaido to watch the speech from the gallery. But his speech otherwise focused little on foreign policy, with no mention of North Korea, a year after Trump used the State of the Union to announce his second summit with the nuclear-armed state's leader, Kim Jong Un.

Trump only briefly mentioned his pro-Israel plan for the Middle East, which he unveiled last week next to Prime Minister Benjamin Netanyahu after more than a year of delay.

On Iran, Trump highlighted his pressure campaign against the clerical regime and boasted of the controversial strike he ordered last month that killed Iran's best-known general, Qassem Soleimani.

"Because of our powerful sanctions, the Iranian economy is doing very poorly," Trump said. "We can help them make it very good in a short period of time, but perhaps they are too proud or too foolish to ask for that help."

Trump in 2018 withdrew from an internationally backed nuclear deal negotiated under his predecessor, Barack Obama, and imposed sweeping sanctions aimed at reducing Iran's regional clout.

 'American comeback'

President Trump hailed the "great American comeback" in a speech to Congress on the eve of his expected acquittal in his impeachment trial.

At his annual State of the Union address, Trump set out his case for another four years in office.

The president refrained from lashing out directly at the lawmakers who have attempted to remove him from office, though he did jab at Democrats.

House Speaker Nancy Pelosi ripped up a copy of his speech behind him.

The Republican president delivered Tuesday night's nationally televised speech in the Democratic-controlled House of Representatives, where he was impeached in December.

On the other side of the Capitol, the Republican-led Senate is all but certain on Wednesday to clear the president of corruption charges in a party-line vote. Republican lawmakers chanted "four more years" as Trump prepared to speak, urging him on for November's White House election.

Before Trump began speaking at the podium in the well of the House, he appeared to snub the outstretched hand of Mrs Pelosi, America's most powerful elected Democrat. The House speaker, critics noticed, skipped the traditional introduction welcoming the president as a "distinct honour".

It was the first time Trump had come face to face with his implacable political foe since she stormed out of a White House meeting four months ago.

When the president accused Democrats of planning to force American taxpayers to provide unlimited free healthcare to undocumented immigrants, Mrs Pelosi was observed twice mouthing: "Not true."

Trump struck an upbeat note in a speech lasting one hour and 18 minutes that contrasted sharply with his lament of "American carnage" in his 2017 inaugural presidential address. In an implicit rebuke to his predecessor Barack Obama, the president told his audience: "In just three short years, we have shattered the mentality of American decline and we have rejected the downsizing of America's destiny. "We are moving forward at a pace that was unimaginable just a short time ago, and we are never going back!"

Trump repeatedly swiped at Democrats, including left-wing candidates such as Bernie Sanders, who are vying to challenge him for the presidency. "We will never let socialism destroy American healthcare!" said the president, whose critics point out that he has not put forward a healthcare plan of his own.

The president invited several special guests to the address, including Venezuelan opposition leader Juan Guaidó, military veterans and the brother of a man killed by an undocumented immigrant.

In a move certain to infuriate liberal critics, Trump announced he would award the Presidential Medal of Freedom, America's highest civilian honour, to firebrand conservative radio host Rush Limbaugh, who revealed this week he has lung cancer.

First Lady Melania Trump bestowed the honour on an emotional Limbaugh as the president spoke.

A protester was escorted from the chamber while Trump defended gun rights. It was Fred Guttenberg, the father of Jaime Guttenberg, a student killed in a mass school shooting at Parkland, Florida, in February 2018.–BBC