NEW YORK - Human Rights Watch has documented mas ked gunmen disabling boats carrying migrants in the Aegean Sea and pushing them back to Turkish waters.

The New York-based international watchdog body said it spoke to nine witnesses who described eight incidents in which masked assailants – often armed – intercepted and disabled the boats carrying asylum seekers and migrants from Turkey toward the Greek islands, most recently on October 7 and 9, 2015. The witnesses said that the assailants deliberately disabled their boats by damaging or removing the engines or their fuel, or puncturing the hulls of inflatable boats. In some cases, the boats were towed to Turkish waters.

Asylum seekers and migrants arrive at the Greek island of Lesbos after being rescued by volunteer Spanish lifeguards when their lives were put at risk by masked men in black uniforms in speedboats who rammed into their rubber raft and removed and threw the engine into the sea. Oct 9, 2015.

“Disabling boats in the Aegean makes an already dangerous journey even more likely to result in death,” Eva Cosse, Greece specialist at Human Rights Watch, said in a statement. “These criminal actions require an urgent response from the Greek authorities.” Human Rights Watch said it also found new cases in which Greek border guards summarily returned migrants and asylum seekers to Turkey across the land border at Evros.

On October 9, Human Rights Watch staff witnessed an overloaded inflatable rubber boat adrift in the waters between Turkey and the Greek island of Lesbos for more than an hour, until a group of Spanish lifeguard volunteers set off on their own boat to rescue them. Right after the rescue, 17-year-old Ali from Afghanistan told Human Rights Watch that their boat had taken off eight hours earlier for Lesbos from the Turkish shore at Assos, packed with men, women, and children. But 30 minutes into their journey, a speedboat suddenly rammed their rubber dinghy. On board were five men dressed in black, their faces covered with balaclavas, armed with handguns.

“At first when they approached, we thought they had come to help us,” Ali told Human Rights Watch. “But by the way they acted, we realized they hadn’t come to help. They were so aggressive. They didn’t come on board our boat, but they took our boat’s engine and then sped away.” The masked men attacked three other boats in quick succession before speeding off toward the Greek coast, Ali said. The boats were packed with asylum seekers mostly from Afghanistan, Syria, and Iraq. The men wore no insignia on their black clothing. “They spoke a language we didn’t know, but it definitely was not Turkish, as we Afghans can understand a bit of Turkish,” Ali said.

Ali said a Turkish coast guard boat approached and took the three women and six children from the rubber dinghy, promising to return for the men on board. Greece is at the forefront of the migrant crisis hitting Europe,with over a half a million migrants and asylum seekers having arrived in the country on their way to richer countries in the EU.

At least 3,135 people have died while making the Mediterranean crossing this year, according to UNHCR.