She also warned against a resurgence of Islamic State group extremists in Syria, saying it "must not" be allowed to happen.

Speaking after talks in Ankara with President Recep Tayyip Erdogan, whose government is in constant dialogue with Hayat Tahrir al-Sham (HTS), she said the EU would increase its own contact with the group that ousted Assad.

"Now we have to step up and continue our direct engagement with HTS and other factions," she said.

European countries are wrestling with their approach to HTS which is rooted in the Syrian branch of Al-Qaeda and has been largely been seen in the West as a terror group, despite moderating its rhetoric.

Earlier this week, the EU sent a senior diplomat to Syria to directly engage with the interim government.

Turkey reopened its embassy in Damascus on Saturday and the EU is also planning to reopen its mission there following "constructive" talks with its new leadership, the bloc's foreign policy chief Kaja Kallas said on Tuesday.

In Ankara, Von der Leyen also warned IS jihadists could reemerge in Syria.

"The risk of a Daesh resurgence... is real. We cannot let this happen," she said, using an Arabic acronym for IS.

Turkey has launched several military operations in Syria since 2016 to battle IS extremists and Kurdish forces, which it views as "terror groups".

Erdogan has often said his government will never allow a "terror corridor" along its border with Syria, with Von der Leyen acknowledging "Turkey's legitimate concerns must be addressed".