A British official says thousands of liters (gallons) of diesel have likely spilled from an oil rig that was blown onto a remote Scottish beach.

The Transocean Winner was being towed when it broke free of its tug and ran aground on the Isle of Lewis on Monday.

The Maritime and Coastguard Agency says two fuel tanks on the rig have been breached.

Hugh Shaw, the government representative for maritime and salvage, said "we're probably talking about a maximum of 52 (metric) tons of diesel oil as the worst-case scenario." That's more than 50,000 liters (13,000 gallons).

Shaw told the BBC Thursday that any oil spill was a concern, "but this is extremely low-risk." He said there was no sign of oil on the ocean surface or coastline.