The vessels were anchored in the neutral waters, outside Russia's territorial waters. "A rescue tug is en route", said a spokesman for the Russian Maritime Agency. One of them, a liquefied natural gas carrier, has exploded. The flames quickly spread to both ships, setting off an explosion aboard one of them.
The explosion happened while the two vessels were sailing in neutral waters near Ukraine and Russian Federation.
"Our vessel "Spasatel Demidov" is extinguishing the fire", the spokesperson said.
"Twelve were rescued, 11 bodies were discovered, nine went missing", Rosmorrechflot told Sputnik, specifying that a total of 32 people were on board the two tankers.
The other one, the Maestro, had a 15-member crew, including seven Turkish nationals, seven Indian citizens and an intern from Libya, Russian news agency Tass quoted the maritime authority as saying.
Severe weather conditions at sea have prevented rescue ships from taking victims to the shore for medical treatment, the report added.
The accident struck close to the Kerch Strait, which has become a new flashpoint in tensions between Russian Federation and Ukraine.
The Kerch Strait between Russian-annexed Crimea and southern Russia controls access from the Black Sea to the Azov Sea, where there are both Russian and Ukrainian ports.
A Russian-built bridge over the Kerch Strait opened in May previous year.