A vast oil spill in the Gulf is quickly becoming one of the world’s worst in years after being allowed to spread almost unchecked for weeks, Reuters reports citing international agencies, satellite imagery and environmental groups.

The slick off the coast of Oman from a grounded tanker carrying Russian crude has reportedly reached the mainland, the UN’s shipping agency tells Reuters.

The slick now covers an area of more than 2,000 square kilometres, says John Amos, an oil spill specialist who reviewed satellite imagery obtained by Reuters.

The Caroline Bezengi, carrying an estimated 800,000 barrels of Russian oil and under international sanctions, ran aground on June 30 at an Omani island that is part of a marine nature reserve. The ship first reported difficulties off Yemen on June 8. Maritime sources said a blast appeared to have occurred aboard the Caroline Bezengi.

No party has claimed an attack, but the vessel was navigating two separate wars on its journey from Russia to India.

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