Greece has no legal justification for suspending asylum procedures as it tries to stop thousands of migrants from Turkey entering its territory, the UNHCR said Monday.
"Neither the 1951 Convention Relating to the Status of Refugees nor EU refugee law provides any legal basis for the suspension of the reception of asylum applications," the UN's refugee agency said in a statement.
Turkey late last week stopped blocking asylum-seekers from trying to reach the EU, effectively suspending a 2016 EU-Turkey deal that had largely stemmed the flow of Syrians, Afghans, Iranians, Iraqis and others that had overwhelmed Greece in 2015.
Turkish President Recep Tayyip Erdogan warned Monday he was allowing "millions" of migrants to head to Europe as he sought to pressure Western countries to back his military operation in Syria.
Greece has deployed its armed forces to prevent migrants crossing its border with Turkey. Prime Minister Kyriakos Mitsotakis on Sunday announced the suspension of new asylum applications for one month.
Exhausted and cold migrants trying to get into Greece have told AFP and other media that Greek border guards have fired tear gas and warning shots to stop them crossing.
Greek residents close to the land border and on one of the islands close to Turkey, Lesbos, have also reacted with hostility to migrants trying to set foot in Greece.
EU leaders including European Commission chief Ursula von der Leyen are to visit the Greek border on Tuesday with Mitsotakis in a show of support for Greece.
UNHCR said "all states have a right to control their borders and manage irregular movements but at the same time (they) should refrain from the use of excessive or disproportionate force and maintain systems for handling asylum requests in an orderly manner".
It said that only the EU as a bloc could decide the emergency measures regarding asylum that Greece was employing, not Athens alone.
"It cannot suspend the internationally recognised right to seek asylum and the principle of non-refoulement (no push-back) that are also emphasised in EU law," it said.
The UN called for boosted international assistance for Greece and Turkey to cope with the migrants they are already hosting as well as new asylum-speakers.
It also highlighted the dire situation in and around the province of Idlib, the main theatre of the intensified conflict in Syria, which required "urgent action" with nearly one million civilians fleeing their homes.