The United States faces difficulties in its withdrawal from Syria, particularly in parting ways with the Kurdish fighters it allied with to battle the armed group ISIL, Turkey's foreign minister said.

"It is hard to break up with a terrorist organisation after being involved with it at this level," Mevlut Cavusoglu told a parliamentary foreign affairs committee on Wednesday.

His remarks came a day after US National Security Adviser John Bolton held talks with officials in Turkey during an apparently tense visit.

Ankara has been infuriated by Bolton's demand for assurances that Turkey will not attack the Washington-allied Kurdish fighters in northeastern Syria before US troops pull out of the complex region.

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"There are different voices coming from different institutions in the US" over the withdrawal process, Cavusoglu said, echoing remarks by Turkish President Recep Tayyip Erdogan on Tuesday.

He suggested closer cooperation with US adversaries was likely on the horizon.

"We want to be in coordination with Western countries - but especially with Russia and Iran during the US withdrawal process. We do not want to create a vacuum for terrorist organisations to use after the withdrawal," said Cavusoglu.

During a visit to Israel on Sunday, Bolton set pre-conditions for the US pullout from Syria that included Turkey guaranteeing the safety of the Kurdish People's Protection Units (YPG), which spearheaded the fight against Islamic State of Iraq and Levant (ISIL, also known as ISIS).

US President Donald Trump announced last month the withdrawal of some 2,000 US troops from Syria in a statement that shocked many politicians in Washington as well as Western and Kurdish allies who fought alongside the US in the war-torn country.

Turkey's criticism

Turkey has long condemned Washington for its military relationship with the YPG. Ankara considers the militia and its political wing - the Kurdish Democratic Union Party (PYD) - to be "terrorist groups" with ties to the banned Kurdistan Workers' Party (PKK) in Turkey.

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Trump's decision to withdraw troops was initially expected to be carried out swiftly, but the timetable became vague in the weeks following his announcement.

Matthew Bryza, a former senior US diplomat, said Washington is looking for a replacement to the Kurdish armed group in the fight against ISIL.

"The YPG has provided up to 50,000 troops - boots on the ground to take the fight directly to ISIS. They fought valiantly and quite successfully. As a result, many American lives were saved," he told Al Jazeera.

"The alternative to the YPG from Washington's perspective is someone else has to come in," Bryza added.

Threat from ISIL

France, Britain and local armed groups have warned ISIL has not totally been defeated yet.

Subsequently, US officials made clear the withdrawal would not happen quickly and would take place in an orderly manner, as the White House faced a backlash from members of the US Congress, and even its own staff.

The US president's withdrawal decision coincided with the resignation of American defence chief James Mattis.

Bryza said Trump's unorthodox ways were likely responsible for the chaos enveloping his Syria plans.

"Donald Trump flip-flops every day on some policy … and he has now allowed his policy to be completely reserved by the statement of National Security Adviser Bolton in Israel," he said.

"My guess is President Trump took his decision on December 14 to pull US troops out of Syria impulsively. He heard something he liked from President Erdogan - that Turkey could take over stabilising Syria and finish the job against ISIS."