Sixteen Navy divers based out of Hawai'i are assisting South Korea after one of its patrol boats exploded and sank last week near contested waters between North and South Korea.

The Navy divers with Mobile Diving and Salvage Unit One are on board the USNS Salvor, a rescue and salvage ship. The divers were in the region for the exercise Key Resolve/Foal Eagle, which ran March 8 to 18.

The Salvor often operates out of Pearl Harbor.

A U.S. Navy cruiser and two destroyers also are on hand. Divers reached the wreckage but were unable to get inside to look for the 46 sailors still missing, the Wall Street Journal reported.

The South Korean ship Cheonan, with a crew of 104, sank in the Yellow Sea.

South Korea's president ordered the military on alert for any moves by rival North Korea after the defense minister said the explosion and sinking of the ship may have been caused by a North Korean mine.

The blast ripped apart the 1,200-ton ship late last week during a routine patrol mission near Baengnyeong Island, along the tense maritime border west of the Korean Peninsula. Fifty-eight crew members, including the captain, were rescued.

The South Korean Joint Chief of Staff said the exact cause was unclear, and U.S. and South Korean officials said there was no outward indication of North Korean involvement.

However, South Korean Defense Minister Kim Tae-young told lawmakers today that a floating mine dispatched from North Korea was one of several scenarios for the disaster.

"Neither the government nor the defense ministry has ever said there was no possibility of North Korea's involvement," Kim said.