The EU has told migrants in Turkey that Europe’s doors are closedas Greek and Turkish police fired teargas at their shared border amid growing tensions over the plight of Syria’s refugees.

In a blunt message, the EU’s foreign policy chief, Josep Borrell, said: “Don’t go to the border. The border is not open. If someone tells you that you can go because the border is open … that is not true.

“Avoid the situation in which you could be in danger … Avoid moving to a closed door,” he said. “And please don’t tell people that they can go because it’s not true.”

Borrell was speaking after a hastily convened meeting of EU foreign ministers in Zagreb, where the bloc restated its criticism of “Turkey’s use of migratory pressure for political purposes”.

Tensions flared last weekend when the Turkish president, Recep Tayyip Erdoğan, declared he was “opening the doors” because Turkey could no longer cope with refugees fleeing Idlib province, the last remaining rebel stronghold in Syria.

Thousands of refugees and migrants have since attempted to reach Greece via its land or sea borders. Greek riot police have been using teargas and water cannon to repel people trying to get into the country, while Turkish police have been firing volleys of teargas towards Greece in return.

Facebook Twitter Pinterest A man picks up a teargas canister fired by police near the Greece-Turkey border. Photograph: Marko Đurica/Reuters

EU ministers met hours after a ceasefire in Idlib came into force, following an agreement in Moscow between Erdoğan and Vladimir Putin on Thursday. Russia and Turkey, on rival sides in Syria’s war, have agreed to preserve some territorial gains made by Russian-backed Syrian forces during the three-month offensive in Idlib, while Turkey keeps a foothold in the region.

On Friday skies in the province were free of warplanes for the first time in three months as the ceasefire appeared to be holding, although clashes before dawn in the south killed six regime soldiers and nine fighters from the Uighur-dominated jihadist group the Turkistan Islamic party, a war monitor said.

Erdoğan said on Friday that Ankara would not abandon its 12 observation posts in Idlib, despite the fact that at least four are now encircled by regime forces and allied militias. What will happen to the posts, which were supposed to monitor a previously agreed 2018 de-escalation line, was notably absent from Thursday’s deal. “The observation points are very, very important for us. They will be preserved as they were in the past,” Erdoğan said.

Facebook Twitter Pinterest Josep Borrell. Photograph: Reuters

On Friday, the EU announced €60m (£52m) in humanitarian aid for civilians in north-west Syria, while warning of the complexities of distributing food, medical supplies and tents in the war-torn region. But EU-Turkey relations are likely to remain in the deep freeze, with no sign of any additional European funds for Turkey, which is hosting nearly 4 million refugees, mostly from Syria.

EU ministers did not agree to add to the €6bn promised in 2016 under the terms of a migration deal with Ankara. The EU has allocated €4.5bn to Syrian refugee aid in Turkey, but only €3.4bn has been spent.

On his return from Moscow, Erdoğan signalled there was no change in policy. “Our gates are open. The refugees will go as far as they can,” Turkey’s state-run Anadolu news agency quoted him as saying.

Turkey has also announced it is sending 1,000 special operations police to prevent Greek authorities from returning people who manage to cross, raising the prospect of vulnerable people trapped indefinitely in a no-man’s land.

Meanwhile, the EU is under fire from human-rights NGOs for accepting Greece’s decision to suspend asylum applications for one month. In an open letter to EU leaders and the Greek prime minister Kyriákos Mitsotákis, 85 charities, including Action Aid and Amnesty International, said they were “deeply concerned” about how authorities were handling new arrivals to Greece.

Facebook Twitter Pinterest A man rides a motorcycle in the north-western Syrian city of Idlib on the first day of a Turkey-Russia ceasefire. Photograph: Omar Haj Kadour/AFP via Getty Images

Greece’s decision to keep its borders shut to asylum seekers is widely supported among EU leaders, who fear a repeat of the 2015 migration crisis, when more than 1 million people arrived in Europe after the German chancellor, Angela Merkel, signalled that the doors were open to them.

Austria’s chancellor, Sebastian Kurz, warned EU states against taking in migrants gathered on the border. “If we do, soon it will be hundreds of thousands and later maybe millions,” he told Funke, a German media group.

Kurz also said that if Greece did not secure its borders, he was prepared to close Austria’s border.

As well as dispatching elite troops to the region, Mitsotákis’ centre-right government also decided to extend the existing 12.5km razor-wire border fence, equipped with sonar systems and thermal sensors, by another 40km, officials said. New sections will be placed in areas believed to be “vulnerable” to passage along the Evros river separating the two countries.

Growing numbers of people have been bussed to the Evros region by Turkish authorities. Despite international criticism of Turkey exploiting migrants for its own political ends, Ankara continued to insist that the land border - unlike the Aegean isles - had never been part of the landmark accord reached in 2016 between Turkey and the EU to stem migratory flows. Indicative of the tensions between the two longstanding regional foes, Erdoğan ruled out meeting Mitsotakis, repeating unproven claims that Greek police had killed at least five migrants in clashes at the land border and were deliberating sinking boatsheaded for the islands. “I don’t want to be in the same place with him,” he was quoted as telling reporters on his return flight from Moscow. “I don’t want to be in the same photograph as him.”

Athens has repeatedly denounced the accusations as “fake news”, saying the movement of migrants was part of a “mass, organised and coordinated operation” to destabilise Greece.

Meanwhile, thousands of Greek-Americans have signed a letter to the US secretary of state, Mike Pompeo, telling him that Erdoğan “is weaponizing migrants who are not even from Syria in order to blackmail Europe. These are not the actions of an ally, a humanitarian, or a responsible global actor. These are the actions of a human trafficker or a terrorist.”