A suspected Muslim extremist shot and killed three American doctors at a missionary hospital in Yemen on Monday, security officials said.

The suspected gunman was later arrested, officials said. No further details were provided.

A fourth American doctor was wounded in the attack in at Maaden hospital in the town of Jibla in Ibb province, 120 miles south of the capital San`a, the officials said on condition of anonymity.

The officials said the attacker was a suspected Muslim fundamentalist who entered the hospital's complex and opened fire with a semiautomatic rifle and a gun.

According to the officials, one of the victims was the director of the hospital. The other two, both women, were the chief doctor and another doctor.

The attacker hid the semiautomatic rifle under his jacket to make it resemble a child and then opened fire, killing the three doctors instantly, the officials said.

He then headed to the hospital's pharmacy and opened fire, wounding the pharmacist, they said.

In Washington, a State Department official said on condition of anonymity that they were aware of the shootings in Yemen, but have no information to give out at this time.

Impoverished, factionalized Yemen has for years been a haven for wanted Muslim extremists and is the ancestral homeland of Al Qaeda terror chief Usama bin Laden. Bin Laden enlisted thousands of Yemenis to fight alongside the Mujahadeen of Afghanistan in their U.S.-backed war against an occupation Soviet army in the 1980s. Many returned when the Soviets withdrew, and they are a powerful political force here.

On Oct. 6, an explosives-laden boat rammed a French oil tanker off the coast of Yemen, killing one member of the tanker's crew, tearing a hole in the vessel and spilling some 90,000 barrels of oil. An intelligence official in Washington has said U.S. experts believed the Limburg attack was the work of unspecified operatives with links to Al Qaeda. Statements attributed to bin Laden and his network's "political bureau" hailed the explosion on the tanker but wouldn't confirm Al Qaeda's responsibility.

The French tanker scenario recalled the Oct. 12, 2000, attack on the USS Cole, which was rammed by a small, explosives-laden boat in the southern port of Aden.

Seventeen U.S. sailors were killed in that attack, which was blamed on Al Qaeda. Al Qaeda also is held responsible for the Sept. 11, 2001, attacks in the United States.

Yemen has signed on as Washington's partner in the war on terrorism launched after the Sept. 11 attacks.

U.S. and Yemeni agents have worked together in a counterterrorism center in Yemen equipped with sophisticated intelligence-gathering facilities. The Americans also have trained Yemeni troops to fight militants. Yemen allows U.S. warships free use of its waters and U.S. warplanes use of its air space.

Yemeni security officials, speaking on condition of anonymity, say up to 3,000 U.S.-trained Yemeni troops have been deployed recently in areas known to harbor wanted Al Qaeda members.

In November, a CIA-operated Predator drone fired a missile that killed bin Laden's top lieutenant in Yemen, Qaed Salim Sinan al-Harethi, and five other Al Qaeda suspects in Yemen.