This photo taken from the Greek side of the Greece-Turkey border near Kastanies shows migrants waiting on the Turkish side on Sunday (AFP photo)

ISTANBUL — Turkish President Recep Tayyip Erdogan warned Monday that "millions" of migrants will soon head for Europe, drawing a sharp rebuke from EU leaders over his efforts to pressure them into greater assistance with the Syrian conflict.

Since Turkey "opened its doors" on Friday for refugees and migrants to leave for the European Union, thousands have massed at the Greek border, triggering fears of another influx like that which poisoned European politics in 2015.

German Chancellor Angela Merkel described Turkey's move as "unacceptable", while EU migration commissioner Margaritis Schinas said "no one can blackmail or intimidate the EU".

But Turkey, which already hosts some four million refugees, is trying to hold off another mass influx from Syria where the Syrian army advancing into the last rebel stronghold of Idlib.

Erdogan said he hoped for a ceasefire in Syria when he meets his Russian counterpart Vladimir Putin later this week.

But he warned Europe that it would share the migrant pressure.

“After we opened the doors, there were multiple calls saying ‘close the doors’. I told them ‘it’s done. It’s finished. The doors are now open. Now, you will have to take your share of the burden’,” he said.

“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.

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.

Erdogan claimed the numbers of migrants at the Greek border, who include Afghans, Syrian and Iraqis, were far higher than figures provided by officials and reporters at the scene. He said there were already hit “hundreds of thousands” there.

“There will be more. Soon, this number will be expressed in millions.”

Greece says some 10,000 were barred from entering the country over the weekend. Clashes broke out as police fired tear gas at the refugees who responded by lobbing rocks.

A video shared by a Turkish official, which could not be independently verified, showed a boat of migrants being shot at and harassed by Greek coastguards.

Turkey also accused Greek police of killing a migrant after a video was shared of a bloodied Syrian on the border, although Athens rejected this as “fake news”.

In desperation, many have sought alternative routes and Greek port police said a young boy died when a makeshift boat capsized off the Greek island of Lesbos.

Athens said it would boost patrols and it suspended asylum applications by those entering illegally — a move denounced by the UN refugee agency as having “no legal basis”.

Turkey agreed in 2016 to stop refugees leaving for Europe in exchange for billions of euros in assistance, and the EU insists that Turkey stick to the deal.

Ceasefire in Idlib?

The migrant question comes as Turkey launched a military operation in Idlib in northwestern Syria in a bid to push back the Syrian army’s offensive.

Close to one million people have been forced to flee the ongoing violence in the biggest wave of displacement of the nine-year conflict, but they are not being permitted into Turkey.

Erdogan and Putin are to meet in Moscow on Thursday.

Despite being on opposing sides of the conflict, they are keen to avoid direct clashes that would jeopardise their broader trade and defence ties.

“I hope that he [Putin] will take the necessary measures there, such as a ceasefire, and that we will find a solution to this affair,” Erdogan said in a speech on Monday.

The Kremlin said cooperation with Turkey was a top priority.

“Our militaries are in constant contact. The main thing is that we now focus on negotiations between Putin and Erdogan,” a spokesman said.

Turkey backs certain rebel groups in Idlib and has observation posts under a 2018 deal with Russia.

But the Syrian army has made steady progress since December, and on Monday, retook the town of Saraqeb, according to the Syrian Observatory for Human Rights, a Britain-based war monitor.

Tensions between Turkey and Syria reached new heights last week when 34 Turkish soldiers were killed in an air strike blamed on Damascus, its heaviest loss since it first intervened in the conflict.

Erdogan said Monday that Syrian losses were “just the beginning” unless it pulled back behind the borders agreed under the 2018 deal.

Damascus responded that it was “determined to confront the flagrant Turkish aggression”.