ANKARA: Greek security forces fired tear gas on Sunday to stop up to 13,000 migrants from crossing the border from Turkey amid a growing crisis over the bloody Assad regime offensive in northwest Syria.

The violence in Idlib province has sent hundreds of thousands of civilians fleeing north toward Turkey, which already hosts more than 3.5 million Syrian refugees and says it can accommodate no more.

Turkish President Recep Tayyip Erdogan has responded on two fronts. First, after an air strike killed 33 Turkish soldiers in Idlib, Turkey launched an offensive to halt the advance of Assad regime forces backed by Russian air power. On Sunday, Turkey shot down two Syrian fighter jets over Idlib and destroyed a military airport in Aleppo, and ground forces exchanged fire.

Second, Erdogan has torn up a 2016 agreement with the EU to halt the flow of refugees from Turkey into Europe, and thrown open the border with Greece. The Turkish president says the EU has not kept to its side of the deal, to pay 6 million euros in aid to Ankara to cope with the influx of migrants.

The announcement triggered an instant rush of thousands of migrants to the border with Greece, which placed crossing points on maximum security alert and deployed riot police at the Kastanies border post.

At least 500 people fled to the Greek islands of Lesbos, Chios and Samos, close to the Turkish coast. On the mainland border, some waded across a shallow section of the Evro River to the Greek side. Authorities in Athens said some migrants prevented from crossing had thrown metal bars and tear-gas canisters at police on the Greek side.

UN refugee agency spokesman Babar Baloch called for “calm and easing of tensions on the border,” and urged countries to “refrain from the use of excessive and disproportionate force.”

Kenneth Roth, executive director of Human Rights Watch, said that instead of being concerned about the relatively few refugees trying to enter Greece, the EU should press Russian President Vladimir Putin to halt the indiscriminate bombing of millions of civilians in northwest Syria.

“If the only alternative is a bloodbath in Idlib, the Turkish government will undoubtedly open its border with Syria, but it is already hosting 3.6 million Syrian refugees so we can expect many people who flee the slaughter to continue on to Greece,” he told Arab News.

The Syrian military was incapable of carrying out this slaughter without the support of Russian bombers, and Putin had the key to end it, Roth said.

“He may well want a refugee crisis in Europe, since his far-right allies would profit. European governments should change Putin’s calculations by imposing targeted sanctions on the Russian officials who are directing these war crimes unless they stop immediately,” he said.

Dr. Christina Bache, visiting fellow at the London School of Economics, said the EU and Turkey should have invested every ounce of influence available to promote an inclusive political settlement when the Syrian war began.

“Syrians have become victims of an increasingly authoritarian Turkey and its failing relationship with the EU,” she told Arab News. “As long as the EU fails to address its own institutional deficiencies in migration management, President Erdogan will exploit rising anti-immigrant sentiment in Europe for the sake of political opportunism.”

Bache said Ankara’s plans to relinquish its responsibility to protect asylum seekers could be violations of the international law principle of non-refoulement, which prevents the return of such migrants to a country where they would be in danger of persecution.

 “A political solution remains the most viable path to reconciliation, justice, and sustainable peace in Syria,” she said.