A large oil spill in the Gulf is quickly turning into one of the world’s worst in years after it was allowed to spread almost unchecked for a couple of weeks, according to international ⁠agencies, satellite imagery and environmental groups.

The slick off the coast of ⁠Oman from a grounded tanker carrying Russian crude had reportedly reached the mainland by Wednesday, the U.N.'s shipping agency told Reuters.

The slick now covers an area of more than 2,000 square kilometers (770 square miles), said 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.