Germany expects Turkey to uphold an EU agreement to prevent migrants reaching the bloc, a spokesman for German Chancellor Angela Merkel said Monday.

The comments come as Ankara sought to maintain pressure on Western countries over the Syrian conflict, warning that "millions" of migrants would soon head toward Europe.

Merkel's German spokesman said Monday a 2016 migrant deal between Turkey and the EU was still in place and should be adhered to.

"We are convinced about the value of the agreement and we expect it to be upheld," Steffen Seibert told reporters in Berlin Monday.

He added that if Ankara is dissatisfied with the deal, then it should address grievances in discussions directly with the EU.

The deal was agreed after a migrant crisis in 2015 that saw waves of refugees arriving on Europe's shores, many who remain in Turkey.

The migrant deal calls for the EU to pay a total of six billion euros ($6.7 billion) to help Turkey accommodate the crowds and hold them back from EU borders.

So far 3.2 billion euros have already been paid out, Seibert said.

Turkey now hosts some four million refugees -- the majority of them Syrians -- but has called for the EU to provide additional support for hosting the migrants.

A fresh surge of migrants has arrived on its border with Greece in recent days after an escalation of fighting in Syria's Iblib province between Turkey and Russian-backed Syrian forces.

Turkey's President Recep Tayyip Erdogan has warned he no longer feels bound by the agreement and had opened its doors to the EU.

"Hundreds of thousands have crossed, soon it will reach millions," he said Monday.

But the numbers remain in dispute.

German's foreign ministry cited a report from the International Organization for Migration that said between 7,000 and 13,000 people remained camped on the Turkish side.

"So far very few people have made irregular crossings," a German foreign ministry spokesman said.