Environmentalists are warning of a potential disaster posed by two Russian oil tankers that ran aground in the ecologically sensitive waters off Ukraine's Moscow-annexed Crimean coastline as local media reported thousands of tons of low-grade fuel has spilled into major Black Sea shipping lane.

Environmentalists are warning of a potential disaster posed by two Russian oil tankers that ran aground in the ecologically sensitive waters off Ukraine’s Moscow-annexed Crimean coastline as Russian officials raced to the site to assess the damage.