The US military informed its counterparts in Baghdad on Monday it was preparing for "movement out of Iraq", a day after the Iraqi parliament urged the government in a non-binding resolution to oust foreign troops.

But hours after the memo was leaked to media the Pentagon put out a statement denying the move, saying the letter was a badly-worded draft.

The head of the US military's Task Force Iraq, Brigadier General William Seely, reportedly sent the letter to the head of Iraq's joint operations command, a copy of which was seen by several news agencies, Daily Mail reported.

"Sir, in deference to the sovereignty of the Republic of Iraq, and as requested by the Iraqi Parliament and the Prime Minister, [the coalition] will be repositioning forces over the course of the coming days and weeks to prepare for onward movement," Seely wrote.

"We respect your sovereign decision to order our departure," the letter said.

President Donald Trump said Sunday aboard Air Force One that troops would not leave Iraq unless the country compensated the US for the costs associated with building and maintaining military facilities there.

"We have a very extraordinarily expensive air base that's there. It cost billions of dollars to build. Long before my time," he said. "We're not leaving unless they pay us back for it."

Trump also said he would punish Baghdad economically if US troops were evicted.

"We will charge them sanctions like they've never seen before ever. It'll make Iranian sanctions look somewhat tame," he warned.

The withdrawal would end America's 17-year military presence in Iraq.

A pullout of US troops could cripple the fight against Islamic State militants and allow the extremists to make a comeback, AP reports. Militants affiliated with IS routinely carry out attacks in northern and western Iraq, hiding out in rugged desert and mountainous areas. Iraqi forces rely on the US for logistics and weapons in pursuing them.

Iraq was barely starting to recover from a devastating four-year war against the Islamic State group when the mass uprising against the country's ruling elite erupted on Oct. 1, forcing the resignation of Prime Minister Adel Abdul-Mahdi two months later. He hasn't been replaced.

An American withdrawal could also enable Iran to deepen its influence in Iraq, which like Iran is a majority Shiite country.

"It is not that simple," Lebanese political analyst Ibrahim Bayram said. "This will increase the complications inside Iraq, the conflicts and contradictions ... and the clash, both political and non-political, between the Iranians and Americans."

The vote Sunday to oust the 5,200 American troops in Iraq requires Iraqi government approval. But it highlights the sharp deterioration in relations between Washington and Baghdad amid soaring tensions between the US and Iran following the US airstrike that killed Iranian Gen. Qassem Soleimani at Baghdad airport.

American forces withdrew from Iraq in 2011 but returned in 2014 at the invitation of the government to help battle the Islamic State group. The extremists had seized vast areas in the north and west of the country after Iraq's armed forces collapsed, including the second-largest city, Mosul.

A US-led coalition provided crucial air support as Iraqi forces, including Iran-backed militias, regrouped and drove IS out in a costly three-year campaign.

Unlike the previous US deployment, which was governed by the Status of Forces agreement that clearly spelled out the rules of termination, American troops in Iraq are now in the country based on a less formal request by the then prime minister, Nouri al-Maliki.

Pressure has been escalating for a US troop withdrawal since the defeat of IS in 2017, particularly among factions loyal to Iran. But calls for their removal grew louder amid outrage over the US strike last week that killed Soleimani along with senior Iraqi militia leaders.

Abdul-Mahdi asked parliament on Sunday to take "urgent measures" to ensure the removal of foreign forces from the country. In a sign of the divisions, the parliament session was boycotted by many Sunni and Kurdish legislators who oppose abolishing the deal with the Americans, and most of the lawmakers who voted were Shiite.

It was not clear what steps Abdul-Mahdi would take following the parliamentary vote. Experts were split on whether, as a resigned prime minister, he has the authority to request the termination of the US presence.

Thafer al-Aani, a Sunni lawmaker, said Abdul-Mahdi doesn't want to risk aggravating the Americans too much by acting alone, which is why he turned to Parliament for backing, adding that the vote was mostly for a domestic audience.

"He feels that America isolated his government by siding with the protesters. ... He decided to side completely with the Iranians after the killing of Soleimani and because of the US position toward the protests," he said.

The US government repeatedly called on the Iraqi government to stop using excessive force on peaceful protesters.

Nearly 500 people were killed by security forces in three months of protests against the country's top political and religious leaders. The protests have also turned into a revolt by the country's Shiites against Iranian influence in the country, with protesters burning Iranian interests in the southern provinces.

On Monday, Abdul-Mahdi met with US Ambassador Matthew H. Tueller and stressed the need for the two countries "to work together to execute the withdrawal of foreign troops from Iraq," according to a statement from his office. In their meeting, Abdul-Mahdi said relations with Washington must be built on a "sound basis."

He didn't elaborate, but said the situation in Iraq was "critical" and that all efforts were being exerted to prevent "sliding towards an open war."

The alarming rhetoric by the two allied nations comes amid a recent series of unclaimed attacks targeting military bases that host U.S. troops in Iraq.

One attack killed an American contractor in Kirkuk late last year, and was blamed on an Iran-backed militia.

That attack sparked a deadly US airstrike targeting that militia, which in turn led to a New Year's Eve assault by militias loyal to Iran on the US Embassy in Baghdad. Abbas Kadhim, head of the Washington-based Atlantic Council's Iraq Initiative, said because Abdul-Mahdi has resigned as prime minister, he didn't want to give the impression that he was acting unilaterally and wanted Parliament to be on board, although he has the right to approve the US troop removal himself.

He said there was no reason the Americans should stay now that the mission to defeat IS is over.

"The troops are there and its called the coalition to defeat ISIS not the coalition to re-occupy Iraq," Kadhim said.

"ISIS was defeated and they have no reason to be there now." Kadhim added that an agreement could be worked out whereby some US trainers can stay behind.

Bayram, the Lebanese analyst, said, however, that Trump's reaction shows that the Americans have no intention of exiting smoothly from Iraq.

"The United States considers its presence in Iraq fundamental, especially since it rid Iraq in 2003 from Saddam Hussein. America also considers itself an essential partner in Iraq," he said.

- additional reporting AP, Daily Mail