Coast Guard aircraft have found no sign of a spill from a Royal Dutch Shell oil drilling barge that ran aground off a southern Alaska island during a fierce winter storm, authorities reported Tuesday.

The 266-foot Kulluk "is sound. There is no sign of a breach of the hull. There is no sign of a release of any product," Coast Guard Capt. Paul Mehler III told reporters Tuesday afternoon.

The rig - a key part in Shell's controversial Arctic oil exploration project - ran aground off Sitkalidak Island, about 200 miles south of Anchorage, on Monday night.

The Kulluk had been working in the Beaufort Sea, off Alaska's North Slope, until October. It was being towed back to its winter home in Seattle when it ran into a severe storm off the Alaskan coast. The Coast Guard evacuated its 18-man crew Saturday night, and it drifted for 10 hours on Sunday after the tug that was towing it lost power.