-- Amnesty International, the human rights advocacy group, wrote to President Bush today to question Washington's deadly missile attack on al Qaeda suspects in Yemen.

Six men suspected of membership in the militant Islamic network died Sunday when their car was hit by a Hellfire missile fired from an unmanned Predator aircraft operated by the CIA.

"If this was the deliberate killing of suspects in lieu of arrest, in circumstances in which they did not pose an immediate threat, the killings would be extra-judicial executions in violation of international human rights law," the London-based group said in a statement. "The United States should issue a clear and unequivocal statement that it will not sanction extra-judicial executions."

The attack, which Deputy Defense Secretary Paul D. Wolfowitz termed "a highly successful tactical operation," killed a leading suspect in the bombing of the destroyer USS Cole two years ago. Seventeen U.S. sailors died in the explosion in Aden, a port in southern Yemen.

U.S. officials blame Osama bin Laden and his al Qaeda network for the Sept. 11, 2001, attacks on the United States as well as the Cole attack.

A Yemeni official said Thursday one of the six suspects killed was a U.S. citizen.

Amnesty said in the statement it also has asked Yemen to clarify whether it had any prior knowledge of the attack. The Pentagon has praised the Yemeni government for cooperating with the United States.