WASHINGTON - The assault on the US consulate in Benghazi last week in which four Americans died was a "terrorist attack" that may have had an al-Qaida connection, a top US counter-terrorism official told Congress on Wednesday.

Rocket-propelled grenades and mortars struck the consulate on Sept. 11, the anniversary of the 2001 attacks on the United States. US Ambassador Christopher Stevens and three other Americans died.

"They were killed in the course of a terrorist attack on our embassy," Matthew Olsen, director of the National Counter-terrorism Center, said in response to a question at a Senate hearing.

Olsen said whether the attack was planned for Sept. 11 was under investigation, but the information so far indicated it was "an opportunistic attack" that "began and evolved, and escalated over several hours."

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