By Lefteris Papadimas and Alkis Konstantinidis

KASTANIES/LESBOS, Greece (Reuters) – European Union officials on Tuesday promised more cash for Greece during a visit to its border with Turkey which tens of thousands of migrants and refugees have been trying for days to breach.

The officials urged Turkey to abide by a 2016 deal which requires it to keep the migrants on its soil in return for EU aid. After an upsurge in fighting in Syria last week, Ankara says it will no longer stop migrants who want to reach Europe.

Greek riot police have used tear gas against the migrants at its Kastanies border post, while the coastguard has tried to stop boats transporting migrants to Greece’s Aegean islands. A Syrian boy died on Monday after his boat capsized in the area.

“The situation at our border is not only an issue for Greece to manage, it is the responsibility of Europe as a whole,” the head of the EU’s executive Commission, Ursula von der Leyen, told a news conference at Kastanies.

“We will hold the line and our unity will prevail,” she said after touring the area with Greek Prime Minister Kyriakos Mitsotakis and the heads of the European Council and Parliament.

Von der Leyen announced additional aid of 700 million euros to help Greece deal with the migrant crisis.

Brussels is desperate to avoid a repeat of the 2015-16 crisis, when more than a million migrants entered the EU from Turkey via the Balkans, straining European security and welfare systems and boosting support for far-right parties.

Greek troops and riot police remained on high alert along the Turkish border on Tuesday, though there were no reports of significant new clashes with the migrants.

“There were only a few attempts today (to cross the border). Let’s hope they get the message,” a machine gun-toting army officer told Reuters at the Kastanies border post.

Army jeeps patrolled the area and roads leading to the Evros river which marks the Greek-Turkish border remained shut.

GREECE, TURKEY AT LOGGERHEADS

The crisis has badly strained ties, never good, between Ankara and Athens.

Mitsotakis accused Ankara of deliberately encouraging migrants to head to the border in order to “promote its geopolitical agenda and divert attention from the situation in Syria”.

He also said these migrants were not fleeing the latest flareup of fighting in Syria’s Idlib province but were people “who have been living safely in Turkey for a long period of time”. Many speak fluent Turkish, he added.

French Foreign Minister Jean-Yves Le Drian also accused Turkey on Tuesday of using the refugees to “blackmail” Europe.

Turkish President Tayyip Erdogan infuriated Mitsotakis on Monday by accusing Greek border guards of killing two migrants and wounding a third, a claim denied by Athens.

On Tuesday, Turkish Foreign Minister Mevlut Cavusoglu said Greek forces were shooting migrants “in the back as they are running away”, but he provided no evidence.

Turkey, which hosts 3.6 million refugees from Syria’s civil war and faces another possible big influx as the fighting drags on there, says it cannot take in any more.

Human Rights Watch said it had received multiple reports that Greek border guards were pushing people back into Turkey, which could violate the right to claim asylum as well as a ban on returning people to where they would be unsafe, both of which are enshrined in international law.

The mood toward migrants on Greek islands such as Lesbos – once relatively welcoming – has soured since the 2015-16 crisis amid a sense that the Athens government and the EU are not providing sufficient support.

“It used to be the island of solidarity but it seems like the locals are exhausted,” said Charlie Meyers, a U.S. aid worker on Lesbos.

(Reporting by Lefteris Papadimas in Kastanies, Alkis Konstantinidis on Lesbos, George Georgioupoulos and Foo Yun Chee in Athens: Ali Kucukgocmen in Istanbul, Gabriela Baczynska in Brussels and Geert de Clercq in Paris; Writing by Gareth Jones; Editing by Janet Lawrence)