Greece is facing renewed scrutiny over claims that members of its coastguard donned masks to threaten migrants into returning to Turkey after online investigators linked them to footage of a recent incident.
In the video, which surfaced this month, unidentified men on a speedboat confront migrants struggling on board a dinghy in the Aegean.
It is the first known recording of such an encounter an was revealed by investigators at German newspaper Der Spiegel, who reported several witnesses claimed they were forced to turn back from the Greek coast.
Greece has denied it is deliberately forcing migrants at sea to abandon their attempts to reach Europe.
The so-called pushback incidents would breach international law.
Athens has also denied that its coastguards wear masks.
But after analysing the video, investigators from Der Spiegel and Bellingcat identified the boat used by the masked men as belonging to the Hellenic Coast Guard.
The row between Greece and neighbouring Turkey over the influx of migrants trying to cross Europe’s eastern frontier has deepened in recent months.
In March, tens of thousands of migrants tried to force their way into Europe, triggering clashes along the border, and Greece has long accused Turkey’s coastguard of doing little to stop migrants trying to reach its shores.
Brussels and Athens accused Ankara of goading migrants to storm the border to "blackmail" Europe into offering more cash and support in the Syrian conflict.
Turkey hosts about 3.6 million refugees from Syria, where its troops and allied rebel forces have battled Russian-backed government troops.
It says the EU has failed to honour promises made to Ankara.
The EU’s chief diplomat, Josep Borrell, visited the land border shared by the two countries on Wednesday, after Athens accused Ankara of encouraging a renewed migration surge.
"Today, following a brief respite due to the pandemic, Turkey has once again declared that its land borders to Europe are open," Greek Foreign Minister Nikos Dendias said.
"At the same time, its coastguard escorts boats laden with migrants to the Greek islands."
"But it also persists in undermining security and stability, as well as peace, in the Eastern Mediterranean. It has caused problems to all its neighbours."
Mr Borrell said the EU was "determined to protect the EU's external borders and strongly support Greece's sovereignty".
"We share your concern. Ee discussed how we could stop the dynamics of escalation," he said.