Barack Obama says the death of US-born al-Qaeda leader Anwar al-Awlaki, is a "major blow" to the organisation.
Awlaki was considered one of the most influential al-Qaida operatives wanted by the United States.
US and Yemen officials say he was killed in a US air strike targeting his convoy Friday morning in Yemen's al Jawf province.
But the killing has sparked debate among legal circles about whether the attack was legitimate because he was put on trial.
Al Jazeera's Rosiland Jordan reports from Washington.