The United States is considering a total withdrawal of U.S. forces from Syria as it nears the end of its campaign to retake all of the territory once held by Islamic State, U.S. officials told Reuters on Wednesday.

Such a decision, if confirmed, would upend assumptions about a longer-term U.S. military presence in Syria, which U.S. Defense Secretary Jim Mattis and other senior U.S. officials had advocated to help ensure Islamic State cannot reemerge.

Still, President Donald Trump has previously expressed a strong desire to bring troops home from Syria when possible.

Major Powers Report Progress on New Syria Constitution Body The foreign ministers of Russia, Iran and Turkey agreed Tuesday to facilitate convening the first session of a committee to draft a new Syrian constitution early next year, saying they hoped it will lead to the launch of a "viable and lasting" peace process.In a joint statement read out by Russian Foreign Minister Sergei Lavrov, they said the work of the committee should be governed by a "sense of compromise and constructive engagement." The foreign ministers of Russia, Iran and Turkey agreed Tuesday to facilitate convening the first session of a committee to draft a new Syrian constitution early next year, saying they hoped it will lead to the launch of a "viable and lasting" peace process.In a joint statement read out by Russian Foreign Minister Sergei Lavrov, they said the work of the committee should be governed by a "sense of compromise and constructive engagement."

The timing of the withdrawal was not immediately clear and U.S. officials who spoke to Reuters on condition of anonymity did not disclose details about the deliberations, including who was involved. It was unclear how soon a decision could be announced.

The Pentagon and White House declined to comment.

The United States still has about 2,000 troops in Syria, many of them special operations forces working closely with an alliance of Kurdish and Arab militias known as the Syrian Democratic Forces, or SDF.

The partnership with the SDF over the past several years has led to the defeat of Islamic State in Syria but outraged NATO ally Turkey, which views Kurdish YPG forces in the alliance as an extension of a militant group fighting inside Turkey.

The deliberations on U.S. troops come as Ankara threatens a new offensive in Syria. To date, U.S. forces in Syria have been seen as a stabilizing factor in the country and have somewhat restrained Turkey’s actions against the SDF.

A complete withdrawal of U.S. troops from Syria would still leave a sizeable U.S. military presence in the region, including about 5,200 troops across the border in Iraq.

Much of the U.S. campaign in Syria has been waged by warplanes flying out of Qatar and other locations in the Middle East.

Still, Mattis and U.S. State Department officials have long fretted about leaving Syria before a peace agreement can be reached to end that country’s brutal civil war, which has killed hundreds of thousands of people and displaced around half of Syria’s pre-war population of about 22 million.

In April, Mattis said: “We do not want to simply pull out before the diplomats have won the peace. You win the fight — and then you win the peace.”

Islamic State is also widely expected to revert to guerilla tactics once it no longer holds territory.

A U.S. withdrawal could open Trump up to criticism if Islamic State reemerged.

Trump has previously lambasted his predecessor, Barack Obama, for the withdrawal of U.S. forces from Iraq that preceded an unraveling of the Iraqi armed forces. Iraqi forces collapsed in the face of Islamic State’s advance into the country in 2014.