The EU border agency Frontex has been complicit in Greece's illegal practices against refugees in the Aegean Sea, German weekly Der Spiegel reported on Friday.

"Breaking the law has become an everyday occurrence at Europe's borders and the EU is allowing it to happen," the weekly said in an investigative report, based on internal official documents, satellite photos and interviews with witnesses.

Greek border guards have long been accused by human rights groups of deliberately abandoning and pushing back refugees at sea.

Der Spiegel published documents showing that Frontex units also observed and even backed these practices in recent months, in violation of international law.

"(Our) research proves for the first time that Frontex officials know about the Greek border guards' illegal practices – and that the agency itself is at times involved in the pushbacks," the weekly reported.

The German weekly documented at least six incidents showing Frontex units were involved in pushbacks near the islands of Lesbos and Samos between April 28 and Aug. 19

While the border agency was required to rescue refugees in overcrowded inflatable boats, Frontex vessels patrolling the area passed them at high speed, creating dangerous waves to force them to return to Turkish shores.

An aircraft belonging to Frontex was also documented passing over refugees who were seeking help at sea, but the border agency sent no one to rescue them.

Der Spiegel's investigative reporting was also backed by Lighthouse Reports, Bellingcat, German public broadcaster ARD, and Japanese broadcaster TV Asahi.