IDOMENI, Greece/NICOSIA (Reuters) - Macedonia dumped about 1,500 migrants and refugees back into Greece overnight after they forced their way across the border, as European nations continued to pass the buck in a migration crisis that risks tearing the European Union apart.

Macedonian soldiers escort migrants who have crossed the border illegally from Greece, into army trucks in the village of Moini, Macedonia March 14, 2016. REUTERS/Ognen Teofilovski

The police action was part of a drive by Western Balkans states to shut down a migration route from Greece to Germany used by nearly a million people fleeing war and poverty in the Middle East and Asia over the last year in Europe’s biggest refugee influx since World War Two.

EU efforts to conclude a deal with Turkey to halt the human tide in return for political and economic rewards hit a setback on Tuesday when EU member Cyprus vowed to block efforts to speed up Ankara’s EU accession talks unless Turkey meets its obligations to recognize its nationhood.

European Council President Donald Tusk, who will chair an EU summit with Turkey on Thursday and Friday, was flying on to Ankara to discuss the fraying pact with Turkish leaders after tough talks with Cypriot President Nicos Anastasiades.

Tusk acknowledged to reporters that the tentative deal put together last week by German Chancellor Angela Merkel and Dutch Prime Minister Mark Rutte with Turkish Prime Minister Ahmet Davutoglu raised legal problems and needed to be “rebalanced” to win acceptance from all 28 EU members.

The European Commission meanwhile postponed proposals to reform the bloc’s flawed asylum system, which puts the onus on the state where migrants first arrive, in an attempt to avoid further controversy before the Turkey deal is finalised.

Some 43,000 migrants are bottled up in Greece, overstraining the economically shattered euro zone country’s capacity to cope, and more continue to cross the Aegean daily from Turkey despite new NATO sea patrols.

An estimated 1,500 people marched out of a squalid transit camp near the northern Greek town of Idomeni on Monday, hiked for hours along muddy paths and forded a rain-swollen river to get around the border fence.

Most were picked up by Macedonian security forces, put into trucks and driven back over the border into Greece late Monday or overnight, a Macedonian police official said.

“It’s a long way from the camp to the mountains, it took me six hours of walking. At my age it was very difficult, I would walk and rest often,” said 60-year-old Mohammad Kattan, who slept rough in the mountains and trekked back on foot.

“My hope was to get to Macedonia, and get my papers stamped so that I could continue on to another country, to Serbia.”

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Greek authorities said they could not confirm the return as there had been no official contact from the Macedonian side. Ties between the two neighbors are fraught because of Greece’s long-standing refusal to recognize Macedonia’s name, which is the same as that of a northern Greek province.

CONDITIONS DETERIORATING

A second group of about 600 migrants was prevented from crossing into Macedonia and many of them spent the night camping in the Greek mountains, according to a Reuters photographer.

At least 12,000 people, including thousands of children, have been stranded in the Idomeni camp, where sanitary conditions have deteriorated after days of heavy rain.

Scuffles have broken out in recent days as destitute people scrambled for food and firewood. Many have been sleeping in the open. Concern about the spread of infection grew after one person was diagnosed with Hepatitis A.

Greek Prime Minister Alexis Tsipras said on Tuesday there was “no chance” that border shutdowns throughout the Balkans would be lifted and urged refugees to move to reception centers set up by the state.

Jan van’t Land, an official with medical charity Medecins Sans Frontieres at Idomeni, said around 400 migrants had returned to the camp.

“There are still many hundreds of people on both the Greek and the Macedonian side of the border,” he told Reuters.

Greek officials say leaflets that circulated at the Idomeni camp before Monday’s march showed it was a planned breakout.

“We are in possession of leaflets that show this was an organized incident, a very dangerous one, endangering people’s lives,” government spokesman George Kyritsis told reporters.

Babar Baloch, regional spokesman for U.N. refugee agency UNHCR who is at Idomeni, said the migrants’ breakout and return “hasn’t solved anything”.

“It just increased sufferings of refugees. It started raining again. The sense of support for refugees in the region is missing,” he said.

Turkey wants its citizens to have visa-free access to Europe by June and to open new “chapters” of its stalled negotiations to join the EU in return for taking back all migrants who cross to Greece or are fished out of its territorial waters.

U.N. and EU officials have doubts about the legality of such a blanket return. Several EU countries, including France, also have misgivings about the visa liberalization, saying Ankara must meet 72 EU criteria before it could be implemented.

And Cyprus is demanding that Turkey must open its ports and airports to Cypriot traffic and recognize the island.

“I conveyed to President Tusk our position that the Republic of Cyprus does not intend to consent to the opening of any chapters if Turkey does not fulfill its obligations as described in the negotiating framework,” Anastasiades told reporters after meeting with Tusk in Nicosia.

Dutch Foreign Minister Bert Koenders, whose country holds the EU’s six-month rotating presidency, said the aim was to find an “intelligent synchronization” between the diplomatic process to reunify Cyprus and the EU-Turkey agreement.