A North Korean ship carrying at least 12 hidden Scud missiles and bound for Yemen has been stopped in the Arabian Sea, U.S. officials said Tuesday. The discovery could be politically explosive. North Korea recently acknowledged it has an active nuclear weapons program in violation of various agreements. Yemen is a Middle Eastern nation that is home to fractious tribes and Islamic extremists.

"The ship was stopped on Monday by Spanish authorities who stopped it in the Arabian Sea about 600 miles from the Horn of Africa. ... It was believed to be bound for Yemen," one official told Reuters.

He said U.S. intelligence had been tracking the ship closely for weeks. CNN reported that the ship had been boarded by U.S. military specialists who were trying to stabilize the cargo.

The Pentagon had no immediate comment.

U.S. officials said the 12 Scud missiles were hidden beneath some concrete. They said other suspicious cargo could be on board but could not say exactly what it was.

U.S. officials said the ship departed from the port of Nam Po and "is a North Korean ship," although it was operating under a different flag, which they declined to identify.

Scud missiles were used by Iraq against Saudi Arabia and Israel during the 1991 Gulf war.

Last August, the United States imposed symbolic sanctions on a North Korean company -- Changgwang Sinyong Corporation -- and the North Korean government for exporting medium or long-range missile components.

Reports at the time said Pynongyang had sold Scud components to Yemen before President Bush came to office in January 2001.

Since North Korea acknowledged in October that it was pursuing a uranium enrichment program, the United States and its allies have halted heavy fuel oil deliveries to the Stalinist state and have cut back on humanitarian food offerings.

But in general, the Bush administration has tried to maintain a patient diplomatic effort to persuade the North to dismantle the nuclear program. Officials have said they had no interest in stirring a crisis with Pyongyang while they are involved in a U.N. arms inspections row with Iraq that could lead to war.

Yemen has long been a country of U.S. concern.

Al Qaeda, the Islamic militant group headed by Osama Bin Laden that is blamed for the Sept. 11, 2001, attacks on the United States, is known to operate in Yemen.

Many al Qaeda adherents were said to seek refuge in Yemen's remote territory after the United States went to war against the extremists group and its ally the Taliban in Afghanistan.

In October 2000, extremists attacked a U.S. Navy vessel in the Yemeni port at Aden, resulting in the death of 17 American servicemen and women.

Defense Secretary Donald Rumsfeld is on a trip to the Horn of Africa this week, trying to enlist regional leaders in fighting terrorism and expanding military cooperation with the United States. The region was shaken by a suspected al Qaeda attack in nearby Kenya last month

PHOTO CAPTION

A North Korean ship carrying at least 12 hidden Scud missiles and bound for Yemen has been stopped in the Arabian Sea, U.S. officials said December 10, 2002. The discovery could be politically explosive. (MapInfo, NASA-Visible Earth/Reuters Graphic)