At least 11 people have died in a fire involving two Tanzanian-flagged cargo vessels in the Black Sea near the Kerch Strait, authorities say.
Russian rescuers are trying to reach sailors who jumped overboard. Fourteen people have so far been rescued.
One ship is a gas tanker, and the fire reportedly followed an explosion, which set the other vessel on fire.
They were named as the Kandy (Venice), with a crew of 17 from Turkey and India, and Maestro, with 14 sailors.
The fire broke out when one vessel was transferring fuel to another, Russian maritime agency spokesman Alexei Kravchenko said, adding that this had then forced several crew members to jump overboard.
Rescue workers reportedly witnessed a further three people struggling in the water, who most likely had drowned.
AFP news agency said that "no signal from either one of the two captains" had been received.
Authorities in the Crimean city of Kerch are now preparing to receive the victims.
The crew members were sailing in "neutral waters" in the Black Sea when the incident occurred, authorities said.
The names of the two vessels, the Venice and the Maestro, both appear on a US treasury list as possible targets for sanctions over petroleum shipments to Syria.
The US tightened sanctions against Syria back in 2011 in response to what it said was President Bashar al-Assad's "continued atrocities" committed against the Syrian people.
The Kerch Strait is a focus of tension between Russia and Ukraine.
In November, Russian border guards seized three Ukrainian naval vessels near the narrow channel, which links the Black Sea with the Sea of Azov.
A court in Russia has extended by three months the detention of 24 Ukrainian sailors captured in the incident. They are accused of illegally crossing into Russian territory.
Ukraine condemned the Russian move, denying that its ships had violated the navigation laws in the area. The strait lies off Ukraine's Crimea peninsula, which Russia annexed in 2014.