Washington ? U.S. forces killed a top associate of Osama bin Laden in Yemen in a missile strike, expanding the war on terror with America’s first overt attack on suspected al-Qaida operatives outside of Afghanistan, a U.S. official said Monday.

Qaed Salim Sinan al-Harethi was one of several al-Qaida members traveling by car in northwest Yemen when a Hellfire missile struck it Sunday, killing him and five others. The official, speaking on the condition of anonymity, said the attack was believed to have been conducted by a CIA aircraft, possibly a missile-carrying Predator drone.

The official Yemeni news agency, local tribesmen and the U.S. official confirmed the strike killed al-Harethi. Witnesses said they saw an aircraft, possibly a helicopter, in the area. Hellfires can also be launched by attack helicopters.

The others killed were believed to be low-level operatives. The attack occurred in the northern province of Marib, about 100 miles east of Yemen’s capital of San’a, where al-Qaida is considered active.

U.S. counterterrorism officials have said al-Harethi, also known as Abu Ali, was al-Qaida’s chief operative in Yemen and a top target of U.S. anti-terrorism efforts. An associate of bin Laden since the early 1990s in Sudan, al-Harethi is a suspect in the Oct. 12, 2000, bombing of the destroyer USS Cole in Aden, Yemen.

The CIA declined comment. On Monday, Defense Secretary Donald H. Rumsfeld told a Pentagon press conference, “It would be a very good thing if he were out of business.”

Besides al-Harethi, at least one more Yemeni al-Qaida operative linked to the Cole attack, Mohammad Hamdi al-Ahdal, is thought to be in Yemen, U.S. officials say. In the Cole attack, two suicide bombers slammed an explosives-laden boat into the hull of the ship, killing 17 U.S. sailors and disabling the vessel.

U.S. intelligence believes Yemeni-based terrorists linked to al-Qaida carried out a similar attack Oct. 6 on a French oil tanker, the Limburg. A small boat apparently crashed into the ship and exploded, blowing a hole in its hull and spilling 90,000 barrels of oil into the Gulf of Aden. One crewman was killed.