MOSCOW (AP) — A Russian freezer trawler with an international crew of 132 sank early Thursday morning in the Sea of Okhotsk off of the Kamchatka Peninsula and at least 54 crew members were killed, rescue workers said.

Emergency services in Kamchatka, citing the head of the rescue operation, said 63 crew members were rescued and the fate of the remaining 15 from the Dalny Vostok trawler was unknown.

More than 26 fishing boats in the area helped to rescue the crew members, emergency services said in a statement on their website. The fishing boats also recovered 54 bodies.

No cause for the sinking was immediately given, but investigators said the ship may have collided with drifting ice.

The Investigative Committee said in a statement that it is considering all theories but it is likely that the trawler hit "an object" floating in the sea.

The accident occurred at about 4 a.m. local time (1800 GMT on Wednesday). The trawler sent no distress signals prior to the sinking, the Interfax news agency said.

The Russian Emergencies Ministry sent an Mi-8 helicopter with rescuers and doctors aboard to deliver medical assistance and transport rescued crew members to hospitals in the city of Magadan, the ministry said on its website. It also set up a telephone hotline for families of the crew.

Among the 132 crew members, 78 are from Russia, 42 from Myanmar and the rest from Latvia, Ukraine and Vanuatu.

Some 1,300 people were involved in the rescue operation, emergency services said.