ATHENS, Greece — A leading international medical charity alleged Thursday that testimony from dozens of migrants over the past two years points to a “recurring practice” of secret, illegal and often brutal deportations back to Turkey from two eastern Greek islands.

Doctors Without Borders said in a new report that the accounts it collected said the forced returns were carried out by uniformed officers or unknown masked individuals. It did not refer to the nationality of the officers mentioned in the accounts.

The report follows charges by charities, activists and Turkish authorities, who alleged similar actions in the Aegean Sea and at Greece’s northeastern land border with Turkey.

Athens has strongly denied such so-called “pushbacks,” and argues that its coast guard has saved hundreds of thousands of migrants from the Middle East and Africa who attempted to reach Greece by crossing in small boats from Turkey.

Greece says it needs to protect its borders, which are also those of the European Union, from mass illegal immigration. In March 2020, Turkey opened its borders into the EU and actively encouraged migrants to cross into Greece.

Doctors Without Borders, which is also known by its French abbreviation MSF, said Thursday that in one case, migrants reported to its staff that two people — including a pregnant woman — allegedly died off the island of Samos when their boat was towed at high speed toward Turkish waters.

“As a medical and humanitarian organization, we could not stay silent in the face of the exceptional scale and severity of the violence reported to our teams” on Samos and the island of Lesbos, the humanitarian organization said. It added that “non-assistance (to migrants), violence and pushbacks have become part and parcel of a system of border management” on the two islands.

Lesbos and Samos, both key landing points for migrants arriving from Turkey, are the only Greek islands where Doctors Without Borders is active.

As a result, according to the group’s report, migrants are turning to alternative, longer voyages that pose a greater risk of hardship or death. There has been an increase in recent years of yachts crammed with migrants leaving Turkey and rounding southern Greece to head for Italy.

Doctors Without Borders said its report drew from accounts by migrants between Aug. 2021 and July 2023. It didn’t cite any first-hand observation of pushbacks by its own teams, but said they had met indications of violence against newly arrived migrants.

It added that the discrepancy between the more than 10,000 arrivals reported to MSF over the two-year period and the nearly 8,000 people actually found “indicate(s) that people unaccounted for by MSF … may have been forcibly returned to Turkey.”

The group said it held anonymous interviews with 56 people who claimed to have suffered illegal deportations. A total of 183 pushbacks were reported, with nine people claiming to have fallen victim to the practice between eight and 14 times.

The report said that while some allegations concerned boats being stopped at sea and towed back to Turkish waters, others said that people who had reached Lesbos and Samos were rounded up before they could claim asylum, mistreated and then dumped offshore on inflatable life rafts.

“From land, testimonies point to a pattern of practices including physical assault, handcuffing, informal detention, groups being forcibly taken to the shore before being pushed back at sea, as well as humiliating strip searches,” it said. The perpetrators were described as “groups of unidentified people with covered faces” who often stole migrants’ phones, money and other possessions.

“MSF has witnessed people running out of the forest screaming, crying and reporting being beaten, and MSF medical staff have treated people on the spot for suspected violence-related injuries,” it said.

In two cases, it said its workers found people who said they had been handcuffed with zip ties by masked men who ran away when they heard the organization’s teams approaching.

“Despite extensive and credible evidence,” Greece and authorities “have failed to hold to account the perpetrators of these violations,” the report states.

In June, the EU border agency asked Athens to provide “clarifications and information” on two reported pushback allegations.