The US-led coalition against the Islamic State group has finished its combat mission in Iraq and will shift to a training and advisory role, Iraq's national security adviser said Thursday.

The change of the mission for around 2,500 American troops stationed in the war-battered country by the end of the year was first announced by US President Joe Biden in July when he hosted Iraqi Prime Minister Mustafa al-Kadhemi.

The Iraqi government has been under pressure from powerful pro-Iranian political groups with armed wings that have vehemently demanded all US troops leave the country.

"We are officially announcing the end of the coalition forces' combat mission," national security adviser Qassem al-Aaraji wrote on Twitter.

"The relationship with the international coalition continues in the areas of training, advising and capacity building" of Iraqi forces, he added.

Aaraji was speaking after a meeting between the coalition and the Joint Operations commanders of the Iraqi security forces.

In effect, the about 2,500 US and 1,000 other coalition troops deployed in Iraq will remain there. They have been acting as advisers and trainers since mid-2020.

IS established a so-called caliphate across swathes of Syria and Iraq from 2014.

It was defeated in Iraq in 2017 after offensives by Iraqi forces with the support of the coalition that has included more than 80 countries, among them Britain, France and several Arab nations.

Even though Iraq declared victory against the IS jihadists in December 2017, the group's remnants still carry out attacks against security forces and civilians and in recent weeks killed several Kurdish fighters in northern Iraq.

Change in messaging

The Hashed al-Shaabi, a former coalition of Iraqi paramilitary groups now integrated into the regular forces, an influential political player and ally of Tehran, is particularly virulent about the departure of American troops.

On social media networks, groups close to pro-Iranian factions have been issuing threats and reminding Washington of a December 31 deadline they have set for a full US withdrawal.

Dozens of rocket and drone attacks have targeted American troops and interests in Iraq in recent months. Never claimed, these attacks are systematically blamed by the United States on pro-Iranian factions.

Washington does not plan to abandon Iraq to the influence of its arch enemy Tehran, with whom it is engaged in a standoff over the Iranian nuclear programme.

Analyst Nicholas Heras of the Newlines Institute in Washington said the United States "continues to have the same military role in Iraq as before, with the major change being the messaging of that role".

"Put simply, the political and security environment in Iraq is so charged that the Biden team wants America to keep a low profile and avoid crises, especially with Iran.

"The White House is well aware that if the United States rocks the boat too much in Iraq, Iran-backed militias will attack US forces, which could ruin American public opinion on staying in the nuclear talks with Iran."

Clandestine presence

Iraqi interior ministry media official General Saad Maan told a news conference on Thursday that "the coalition will have completely finished the transition to a non-combat mission before the end of the year".

He was quoting what the coalition commander, Major General John W. Brennan Jr., had said during their meeting.

The majority of US troops sent to Iraq in 2014 as part of the coalition were withdrawn under president Donald Trump.

But Iraq remains an important link for Washington's strategic posture, particularly for anti-jihadist operations in neighbouring Syria.

A UN report early this year said the IS maintains some 10,000 fighters in Iraq and Syria and conducts a sustained insurgency on both sides of the border.

The coalition insists it is in Iraq at the invitation of the government, its troops now stationed at three Iraqi bases managed by Iraqi forces.

In recent months, it has made numerous announcements highlighting its change of mission.

In November, it underlined in a press release the departure from Iraq of more than 2,100 trucks carrying military equipment.