ANKARA (AP) -- Facing a wave of nearly a million people fleeing fighting in northern Syria, Turkey has thrown open its borders with Greece to thousands of refugees and other migrants trying to enter Europe, and has threatened to send "millions" more.
Greece responded by closing the land border, rushing in military and police reinforcements, and tried to stop migrant boats attempting the short but perilous crossing from the Turkish coast to its eastern islands.
Human rights organizations have called for urgent action to stop the situation from deteriorating further, warning of an unfolding humanitarian crisis.
Here is a look at the situation at the border, and at whether this the beginning of another migration crisis for Europe.
WHO ARE THE MIGRANTS GATHERED AT THE GREEK BORDER?
Turkey hosts 4 million refugees, some 3.6 million of them from Syria. Previously, their movement inside Turkey was strictly regulated and under a 2016 deal with the European Union, Turkey tightened border controls. Since Ankara announced last week that it would not impede those seeking to enter Europe, thousands of Afghans, Iranians, Syrians, Pakistanis and others from Africa and Asia have rushed to try their luck.
Although the push ostensibly stems from the conflict to Turkey's south, Greek officials say very few of the recent arrivals are Syrians. Most of those arrested Monday were Afghans, Pakistanis and Moroccans. Figures from January, before the intensified fighting in Syria, show 35 percent of those who entered Greece from Turkey were Afghans. Syrians accounted for 14 percent.
HOW MANY HAVE CROSSED INTO GREECE?
By late Monday, Greek authorities had arrested and charged 183 people with illegal entry after crossing the land border with Turkey. Some 24,000 attempts to pass have been thwarted since Saturday. Nearly 1,000 arrived on the Greek islands in the 24 hours up to Monday morning. According to the U.N.'s International Organization of Migration, 13,000 had gathered at the 212-kilometer (132-mile) border by Saturday evening. Turkey, meanwhile, says that more than 100,000 refugees have left its territory but there is no evidence to support this claim. Uneasy NATO allies Greece and Turkey are historic regional rivals who came close to war three times in the past half-century, and even before this crisis relations were tense over undersea exploration rights.
WHY HAS ERDOGAN OPENED THE GATES?
Turkey has long complained about the lack of support it receives for shouldering the burden of caring for the world's largest refugee population. Despite the promise of 6 billion euros to pay for services for Syrians, Turkish President Recep Tayyip Erdogan wants to renegotiate the deal with the EU. He says Turkey has spent $40 billion to date on hosting refugees. Ankara also seeks support for its policy in Syria, where it opposes Syrian President Bashar Assad and Kurdish fighters linked to the PKK, which has fought a 35-year insurgency inside Turkey. Erdogan wants to use some territory seized from the Kurds in October to resettle refugees from Turkey but the plan has met with little international support.
COULD THIS BE 2015 ALL OVER AGAIN?
In 2015 a million refugees reached Europe, crossing mainly from Turkey to Greece, and to a lesser degree from countries such as Libya to Italy. Although Erdogan said Monday that "millions" would soon be waiting to cross the Greek border, EU border states such as Greece and Bulgaria have quickly mobilized police, border guards and the military to deal with the scenario and seem better prepared to halt large-scale land crossings than in 2015. Sea crossings, however, are much harder to stop. With the Turkish coast guard doing nothing to halt migrant boats heading for the Greek islands, once the flimsy, overcrowded vessels are inside Greek waters they can't be turned back. Very often, their occupants need to be rescued from sinking or crippled boats. Late last year arrivals in Greece were at their highest level since 2016, even before Turkey removed its border controls, and the EU fears a repeat of the crisis that triggered divisions among member states.
WHAT DOES THIS MEAN FOR GREECE?
Even before the current crisis, Greece was struggling to cope with tens of thousands of migrants who had entered from Turkey. Most want to continue to more prosperous EU countries such as Germany, but are stuck in Greece following border shutdowns in countries further along their route. Island migrant camps are many times above capacity -- more than 20,000 people are on Lesbos alone -- and living conditions there are dire. Under the EU-Turkey deal, new arrivals must stay on the islands until their asylum bids are processed, but the lengthy asylum process has led to a big backlog. Island residents are running out of patience after five years of bearing the brunt of Europe's migrant influx, and Greek government efforts last week to build new detention camps on Lesbos and Chios provoked riots on the islands.