SANAA, Yemen - US-born cleric Anwar al-Awlaqi, a prominent al-Qaida chief described by US officials as "the most significant risk" to the United States, was killed on Friday in what analysts called a "significant blow".

A senior US official confirmed Awlaqi's death after an announcement by the Yemeni defense ministry.

"I can confirm ... he's dead," the senior administration official said, without providing further details.

In Sanaa, the defense ministry said Awlaqi was killed on Friday morning but did not elaborate on the circumstances of his death.

Tribal sources said that Awlaqi, who was on a US wanted list, was killed in an air strike on two vehicles in Marib province, an al-Qaida stronghold in eastern Yemen, early in the day.

Several other suspected al-Qaida operatives were also reported killed.

One tribal source said that the plane that launched the sir strike was likely to have been American.

"US planes have been flying overhead for days now," said the tribal source who requested anonymity.

"Then this morning, at about 9:30, what appeared to be a US aircraft fired on the two cars Awlaqi and his fellow operatives are believed to have been traveling in," he said.

US Republican Representative Peter King, chairman of the House Committee on Homeland Security, called Awlaqi's killing "a great success in our fight against al-Qaida and its affiliates".

"For the past several years, Al-Awlaqi has been more dangerous even than Osama bin Laden had been. The killing of al-Awlaqi is a tremendous tribute to President (Barack) Obama and the men and women of our intelligence community," he said.

Al-Qaida leader bin Laden was killed when US special forces raided his compound in Pakistan on May 2.

Another tribal source, also on the condition that he not be identified, spoke of rumors that Awlaqi had recently changed locations within Yemen.

Up until three weeks ago, he had been believed to be hiding out in the southern Shabwa province, another militant bastion.

"But then word came that Awlaqi was in fact in Marib province, a move he made sometime in the last three weeks," the source said.

The source added that Yemeni security forces have been more actively seeking Awlaqi in Marib since the speculation that he had moved.

He said Awlaqi, feeling threatened by the boosted efforts to capture him, "fled Marib last week to hide out in the nearby al-Jawf province" on the Saudi-Yemeni border.

A US-based group specialized in monitoring jihadist organizations described Awlaqi's death as a "significant blow to al-Qaida in the Arabian Peninsula."

IntelCenter said in a statement that Awlaqi's death "would especially impact the group's ability to recruit, inspire and raise funds".

Agence France-Presse