ANKARA

With the bloc facing accusations of not keeping its promises, the amount the EU has paid to support Syria refugees in Turkey must be clarified, said a top European Union leader on Tuesday. 

The March 2016 deal between Turkey and the EU on migration was an "important and complex" one, European Commission President-elect Ursula von der Leyen told a press conference in Brussels.

Von der Leyen said EU has been willing to pay the €6 billion ($6.6 billion) it pledged for refugees in Turkey but that there is a debate over whether the whole sum has been paid out or not.

"There are different numbers out there. I think numbers have to be clarified. Because we are all accountable to that," she stressed.

The 2016 deal aimed to discourage irregular migration through the Aegean Sea by taking stricter measures against human traffickers and improving the conditions for the 3 million -- now 3.6 million -- Syrian refugees in Turkey.

Turkey has complained that the EU failed to uphold its side of the deal, including visa liberalization for Turkish citizens and the millions of euros in aid for Syrian refugees.

Last week Turkish President Recep Tayyip Erdogan -- a longtime critic of EU failures to keep its promises -- warned that Turkey could "open its doors" to let Syrian refugees to cross into Europe if Ankara does not get the support it expects.

The EU had pledged €6 billion ($6.6 billion) aid to improve living conditions of Syrian refugees in Turkey, but only €2.22 billion ($2.45 billion) were disbursed as of this June, according to Turkey.

Turkey currently hosts some 3.6 million Syrian refugees, more than any other country in the world.