BERLIN: Europe's border security agency Frontex has been involved in several illegal "pushbacks" of asylum seekers crossing the Aegean Sea from Turkey to Greece, media including Germany's Der Spiegel reported Saturday.
The investigation "shows for the first time that senior Frontex officials know about illegal practices by Greek border guards -- and that some of them are themselves implicated in pushbacks," the weekly said on its website.
Also known as refoulements, "pushbacks" are incidents where refugees or asylum seekers are illegally returned across a border to a country where they could face persecution.
Journalists say they uncovered six cases since April when Frontex units at a minimum did nothing to stop refugee boats in Greek waters being returned towards Turkey.
A video from a June incident shows a Frontex boat blocking a refugee boat, with a later shot from the same encounter shows it racing across the bow of the migrant boat before leaving the area.
German public broadcaster ARD, journalist collective Lighthouse Reports, investigative platform Bellingcat and Japanese broadcaster TV Asahi were involved in the investigation alongside Der Spiegel.
The journalists say they compared "dozens" of videos, also checking satellite imagery and eyewitness accounts from both refugees and Frontex workers.
Spiegel reported that more than 600 people from the European border agency equipped with boats, drones and aircraft are deployed in Greece, where many migrants first enter the EU.
It added that Frontex would not comment on the individual cases uncovered by the investigation, but referred to a human rights and non-refoulement code of conduct supposed to bind staff.
The agency posted on Twitter Friday that its actions in support of Greek authorities were "in full respect of fundamental rights and international law," adding that it "has been in contact with the Greek authorities about some incidents at sea in recent months".
Athens had launched an "internal inquiry," it added.
Greece's conservative government has always rejected claims of illegal pushbacks taking place at its borders, regularly alleged by several charities. "Our country protects its borders with an absolute respect for international law," Greek Immigration Minister Notis Mitarakis said on Saturday.