US President Barack Obama has declared the killing of a fiery American-born cleric a “major blow” to al-Qaida’s most active affiliate and vowed a vigorous US campaign to prevent the terror network and its partners from finding a haven anywhere in the world.

An American-born cleric killed in Yemen played a “significant operational role” in plotting and inspiring attacks on the US, officials said, as they disclosed detailed intelligence to justify the killing of a US citizen.

Anwar al-Awlaki, a US-born Islamic militant cleric who became a prominent figure in al-Qaida’s most active branch, has been killed in the mountains of Yemen.