Turkey using refugees to pressure EU 'unacceptable': German Chancellor Angela Merkel

German Chancellor Angela Merkel said Monday it was "unacceptable" for Turkey to pressure the EU "on the backs of refugees" as thousands, some fleeing fighting in northern Syria, sought to enter the bloc.

"I find it completely unacceptable that... President Erdogan and his government did not bring their dissatisfaction to us at the EU, but instead duked it out on the backs of refugees," Merkel told a Berlin press conference, while acknowledging the "additional burden" on Turkey.

Meanwhile EU migration commissioner Margaritis Schinas said "no one can blackmail or intimidate the EU" at a separate Berlin event.

"Each time the EU is tested as it is now, unity must prevail," Schinas added. President Recep Tayyip Erdogan has warned he no longer feels bound by a 2016 deal to hold refugees in Turkey in exchange for billions in EU cash.

"Hundreds of thousands have crossed (into the EU), soon it will reach millions," he said Monday.

But the numbers remain in dispute.

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

"For me the option is that we talk to Turkey so that we get back to the situation we had before, namely that Turkey fulfils its obligations with our support, even as the burden has grown," Merkel said.

More intense fighting in Syria's Idlib province between Turkey and Russian-backed Syrian forces has contributed to an increase in the numbers of refugees fleeing the conflict.