KASTANIES, Greece (AP) — Clashes erupted on the Greek-Turkish border Friday morning, with Greek authorities using tear gas and a water cannon to repulse an attempt by migrants to push through the frontier into Greece, while Turkish authorities fired volleys of tear gas onto the Greek side of the border.

Thousands of migrants and refugees have been trying to get into Greece through the country’s eastern land and sea borders over the past week, after Turkey declared its previously guarded borders with Europe were open.

After months of threats, Turkish President Recep Tayyip Erdogan said his country would no longer be the gatekeeper for Europe. He has demanded Europe shoulder more of the burden of caring for refugees, although the EU insists it is abiding by a deal in which it disbursed billions of euros for care in return for Turkey keeping the refugees on its soil.

His decision and its aftermath on the border with Greece have alarmed governments in Europe, which is still seeing political fallout from mass migration that started five years ago.

Erdogan's move to open the border came amid a Syrian government offensive in Syria’s northwestern Idlib province, where Turkish troops are fighting. The Russia-backed offensive has killed dozens of Turkish troops and sent nearly a million Syrian civilians toward Turkey’s sealed border.

A cease-fire in Idlib brokered by Erdogan and Russian President Vladimir Putin on Thursday went into effect at midnight. Opposition activists and a war monitor reported a complete absence of Russian and Syrian government warplanes in the skies of Idlib and a relative calm in the area. It was not clear whether the agreement would also affect the situation on the Turkish-Greek border.

Turkey currently hosts more than 3.5 million Syrian refugees, and Erdogan had frequently threatened to open Turkey's borders to Europe. He maintains the EU has not upheld its end of a more than 6 billion-euro deal designed to stem the flow of migrants into Europe, after more than a million people entered the EU in 2015.