The U.S. Coast Guard had plans to sink a derelict Japanese vessel drifting toward Alaska that was washed out to sea by last year's devastating tsunami, but has postponed the operation for now, a spokesman said on Thursday.

Plans to use explosives to send the fuel-laden ship to the ocean floor were on hold because there is a fishing vessel nearby, U.S. Coast Guard Chief Petty Officer Kip Wadlow said.

The Coast Guard is waiting for that vessel to clear out of the area.

Our focus continues to be to ensure the safety of mariners, he said, adding that the Coast Guard was continuing to evaluate the best way to manage the drifting 200-foot vessel, named the Ryou-Un Maru. The Ryou-Un Maru, nicknamed a ghost ship for its abandoned state, is among the 1.5 million tons of debris the Japanese government estimates was dragged out to sea by last year's tsunami, said Ben Sherman, a spokesman for the National Oceanic and Atmospheric Administration.

This boat, in this case, we know was at a particular pier, and before the tsunami it was there and after the tsunami it wasn't, Sherman said.

Experts from NOAA and other agencies have determined that sinking the ship is the best way to manage the potentially dangerous fuel on board, Sherman said. They anticipate that it'll dissipate or evaporate very quickly, he said.

Although most of the tsunami debris expected to hit U.S. coastlines is predicted to arrive in 2013 or later, some items have already washed ashore. In Alaska, most of the marine debris identified as tsunami-related has been buoys and floats from oyster farms.

The Ryou-Un Maru, carrying up to 2,100 gallons of diesel fuel, is about 170 nautical miles southwest of the Alaskan town of Sitka and is drifting toward busy navigational lanes used by cargo vessels plying the waters of the Great Circle route between North America and Asia, the Coast Guard's Wadlow said.

The Great Circle is so-named because it arcs from the U.S. West Coast to East Asia, passing through the Aleutian islands.

The ship was initially spotted by Canadian officials in waters off the coast of British Columbia, Wadlow said. It drifted into U.S. waters on Saturday, and the U.S. Coast Guard began its close monitoring of the vessel.

The ship in question lacks lights, making it a dark obstacle at night dangerous to mariners, Wadlow said.

The Coast Guard confirmed the location with an overflight Wednesday and has dropped a navigational buoy to better track its movements. The ship was set adrift after a magnitude 9.0 earthquake off Japan's northeast coast on March 11, 2011, triggered a 75-foot (23-metre) wall of water that flattened waterfront towns, killing about 16,000. Three thousand people are still missing.

U.S. authorities were immediately aware that the clockwise circulation of the Pacific's northern waters would deliver some remnants of that destruction.

Wadlow said the ship's owner does not want the Ryou-Un Maru back, and the Coast Guard has the legal responsibility to eliminate the navigational hazard it poses. The owner was notified and basically expressed that they were not interested in salvaging the vessel, Wadlow said.

(Editing by Alex Dobuzinskis, Cynthia Johnston and Todd Eastham)