OSLO, Norway -- The Norweigian owners of a tanker claim an unidentified object it collided with in the western Mediterranean was a U.S. nuclear submarine.

Shipping company Leif Hoegh said on Friday the hull of its tanker, the Norman Lady, was damaged in the incident two days ago.

The company said the vessel, which had just unloaded a cargo of explosive natural gas in Barcelona, Spain, struck a submerged object.

The collision took place at the same time and place as the U.S. Navy reported a collision between its Oklahoma City attack submarine and an unknown merchant vessel.

No one on either vessel was hurt.

There had been no leaks of oil from fuel tanks and no threat to the environment.

Leif Hoegh president Thor Joergen Guttormsen told Reuters that there was a "strong likelihood" that the two collided.

He said: "We can't be absolutely certain, we are awaiting a report from the U.S. authorities."

The Norman Lady was built in 1973 and can carry 87,000 cubic metres of liquefied natural gas.

"The tanks are high above the hull and are built to withstand collisions like this," Guttormsen said.

It is now anchored off Gibraltar where divers were planning to inspect the damage.

The U.S. navy said on Wednesday that the Oklahoma City's "sail" command and control area on top of the submarine and its periscope were damaged in a collision as the submarine was rising to periscope depth east of the Strait of Gibraltar.

In describing the known damage to the sub, officials in Washington said the radar mast on the sail section would not raise, one of the periscopes would not lower and some doors to the sail were jammed.

The Oklahoma City is a Los Angeles-class attack submarine commissioned in 1988 and powered by one nuclear reactor.

It normally has a crew of 12 officers and 115 enlisted sailors and is armed with Tomahawk cruise missiles, Mk-48 torpedoes and Harpoon missiles.

Last year, the attack sub USS Greenville collided with a Japanese trawler near Hawaii. Nine people died on board the boat died when it sank.