MANILA: A U.S. Navy minesweeper ran aground on a coral reef in the Philippines on Thursday, but there were no injuries to the crew and Philippine authorities were trying to determine if the ship caused damage to a marine park in a protected area.

The Navy said in a statement that the crew of the USS Guardian was working to find out the best method of safely extracting the ship.

It had just completed a port call in Subic Bay, a former American naval base west of the Philippine capital, when it hit the reef in the Tubbataha National Marine Park, a World Heritage Site in the Sulu Sea, 640 kilometers (400 miles) southeast of Manila.

The ship was not listing or leaking oil but about 15 percent of the bow appeared to have struck the reef, said Angelique Songco, head of the government's Protected Area Management Board, after flying over the ship in a Philippine Air Force plane. "It does not appear to be damaged."

She said it was unclear how much of the reef was damaged. She said the government imposes a fine of about $300 dollars per square meter (yard) of corals that are damaged.

In 2005, the environmental group Greenpeace was fined almost $7,000 after its flagship, the Rainbow Warrior, struck a reef in the same area.

Songco said that park rangers were not allowed to board the ship for inspection and were told to contact the U.S. Embassy in Manila. Their radio calls to the ship were ignored, she said.

She said the ship may be able to float free during a high tide later Thursday.

U.S. Navy ships have stepped up visits to Philippine ports for refueling, rest and recreation, and joint military exercises as a result of a redeployment of U.S. forces in the Asia-Pacific region. The Philippines, a U.S. treaty ally, has been entangled in a territorial dispute with China in the South China Sea.