BEIRUT (AP) — An oil spill caused by leakage from a U.K.-sanctioned tanker grounded for weeks off Oman appears to be expanding dramatically, reaching shorelines and far out to sea, according to experts and satellite images reviewed by The Associated Press. This was reported by Qazaqyia.kz citing Associated Press.

Greenpeace Germany said in a statement Monday that satellite images from a day earlier indicate the oil spill now covers an estimated 150 square kilometers (58 square miles), affecting large stretches of Qibliyah Island off Dhofar, Oman’s largest governorate.

Compared to satellite images from a week earlier, “it is a drastic increase,” said Nina Noelle of Greenpeace Germany, who noted that clearly a large amount of crude oil is leaking. Last week, the spill’s surface area was estimated at 20 square kilometers (8 miles.) It was not clear what has caused the leak to grow.

The images from Sunday showed an oil sheen spreading to the northeast from the 274-meter (899-foot) Suezmax tanker Caroline Bezengi, which is sanctioned by the U.K. for carrying oil that originates from Russia.

The affected area is part of the Arabian Sea reserve, a marine protected area and host to wildlife including endangered petrels and the rare Arabian Sea humpback whale.

Wim Zwijnenburg, an environmental expert for PAX, a Dutch organization that focuses on conflict and the environment, said the sheen is a thin layer of oil that often evaporates depending on the type of crude oil and weather conditions. Thick black patches of oil reached the southern and western shores of the island, he added.

Zwijnenburg said the oil sheen appears to be roughly 90 kilometers long (56 miles), nearly double its length a week ago.

He estimated that the tanker had been carrying over 800,000 barrels of crude oil.

The tanker has been grounded since June, according to two shipping and maritime news outlets which reported that the crew reported an explosion on board at the time. The AP was not able to independently confirm the reports.

The U.K. government said in its decision to sanction the vessel that it “has been or is likely to be involved in activity whose object or effect is to destabilize Ukraine.”