About 1,300 tons of fuel oil have leaked near the Black Sea after a Russian oil tanker split in half – in a storm that sank three other ships.
A Russian official said the tanker accident was a "very serious environmental disaster".
The vessel came apart after it was smashed by 5m (16ft) waves at the Kerch Strait between the Azov and Black Seas.
The weather is hampering efforts to rescue its 13 crew, as well as up to 10 sailors missing from two other ships.
Dozens of vessels have reportedly been evacuated from the busy Russian commercial port of Kavkaz because of the storm, which was packing winds of 108km/h (67 mph).
See the BBC’s full report.