ISTANBUL/BEIRUT (Reuters) - Turkey will take over the fight against Islamic State militants in Syria as the United States withdraws its troops, President Tayyip Erdogan said on Friday, in the latest upheaval wrought by Washington’s abrupt policy shift.

The surprise announcement by U.S. President Donald Trump this week that he would withdraw roughly 2,000 troops has felled a pillar of American policy in the Middle East. Critics say Trump’s decision will make it harder to find a diplomatic solution to Syria’s seven-year-old conflict.

For Turkey, the step removes a source of friction with the United States. Erdogan has long castigated his NATO ally over its support for Syrian Kurdish YPG fighters against Islamic State. Turkey considers the YPG a terrorist group and an offshoot of the armed Kurdistan Workers’ Party (PKK), fighting for Kurdish autonomy across the border on Turkish soil.

In a speech in Istanbul, Erdogan said Turkey would mobilize to fight remaining Islamic State forces in Syria and temporarily delay plans to attack Kurdish fighters in the northeast of Syria - shifts both precipitated by the American decision to withdraw.

The news was less welcome for other U.S. allies. Both France and Germany warned that the U.S. change of course risked damaging the campaign against Islamic State, the jihadists who seized big swathes of Iraq and Syria in 2014-15 but have now been beaten back to a sliver of Syrian territory.

Likewise, the U.S.-backed militia spearheaded by the YPG said a Turkish attack would force it to divert fighters from the battle against Islamic State to protect its territory.

A U.S. official, speaking on condition of anonymity, said American troops may continue to operate against Islamic State in Syria. The Pentagon is considering using Special Operation teams based in Iraq to target militants in Syria, the official said.

The official emphasized that using special operators on the ground was one of many options being considered, was still in the planning stages and that no final decision had been made.

Islamic State launched an attack on Friday in Syria’s southeast against the U.S.-backed SDF militia, employing car bombs and dozens of militants.

“We will be working on our operational plans to eliminate ISIS (Islamic State) elements, which are said to remain intact in Syria, in line with our conversation with President Trump,” Erdogan said.

The Turkish president had announced plans last week to start an operation east of the Euphrates River in northern Syria to oust the YPG from the area that it largely controls. This week, he said the campaign could come at any moment. But on Friday, he cited the talk with Trump as a reason to wait.

FILE PHOTO: Turkish President Tayyip Erdogan speaks during a joint news conference with his Iranian counterpart Hassan Rouhani (not seen) after their meeting in Ankara, Turkey, December 20, 2018. REUTERS/Umit Bektas

“Our phone call with President Trump, along with contacts between our diplomats and security officials and statements by the United States, have led us to wait a little longer,” he said.

“We have postponed our military operation against the east of the Euphrates river until we see on the ground the result of America’s decision to withdraw from Syria.”

Erdogan said, however, that this was not an “open-ended waiting period” and that, due to past “negative experiences”, Ankara welcomed the United States’ statements with an equal amount of pleasure and caution.

Turkey has repeatedly voiced frustration over what it says is the slow implementation of a deal with Washington to pull YPG fighters out of Manbij, a town in mainly Arab territory west of the Euphrates in northern Syria.

The United States will probably end its air campaign against IS in Syria when it pulls out troops, U.S. officials have said. Erdogan’s foreign minister said the withdrawal plan would be discussed by the two countries in Washington in January.

‘TIME FOR OTHERS TO FIGHT’

Trump maintained that IS had been wiped out, a view not shared by key allies, that Washington had been doing the work of other countries and it was “time for others to finally fight”.

His defense secretary, Jim Mattis, opposed the decision and abruptly announced on Thursday he was resigning after meeting with the president.

In a candid letter to Trump, the retired Marine general emphasized the importance of “showing respect” to allies that have voiced surprise and concern about the president’s decision.

Russia said on Friday it did not understand what the United States’ next steps in Syria would be, adding that chaotic and unpredictable decision-making in Washington was creating discomfort in international affairs.

Several of Trump’s fellow Republicans in Congress, joined by opposition Democrats, urged the president to reverse course, saying the withdrawal would strengthen the hand of Russia and Iran in Syria and enable a resurgence of Islamic State.

Trump has given no sign of changing his mind. He promised to remove forces from Syria during his 2016 election campaign.

The roughly 2,000 U.S. troops in Syria, many of them special forces, were ostensibly helping to combat Islamic State but were also seen as a possible bulwark against Syrian President Bashar al-Assad, who has retaken much of the country from his foes in the multi-sided civil war, with military help from Iran and Russia.

IS declared a caliphate in 2014 after seizing parts of Syria and Iraq. The ultra-hardline Sunni militants established their de facto capital in the Syrian city of Raqqa, using it as a base to plot attacks in Europe.

A senior U.S. official last week said Islamic State was down to the last 1 percent of the territory it once held. The group has no remaining territory in Iraq, though militants have resumed attacks since their defeat there last year.

Islamic State launched an attack on Friday on positions held by the SDF in Syria’s southeast and the U.S.-led coalition mounted air strikes in the area, an SDF official said.

Kurdish-led forces in northern Syria may not be able to continue to hold Islamic State prisoners if the situation in the region gets out of control after a U.S. pullout, top Syrian Kurdish official Ilham Ahmed said on Friday.