President Barack Obama said the killing of US-born cleric Anwar al-Awlaqi is a "major blow" to Al-Qaeda's Yemeni outfit and vowed to be relentless in destroying global terror networks.

In Sanaa, the defence ministry said Awlaqi, an Al-Qaeda leader wanted over attacks in the US, was killed on Friday morning, while a man wounded in the attack was quoted as saying seven people were killed in the air strike in Marib province, a hotbed of Al-Qaeda activity.

The ministry said among those killed was Pakistani-American Samir Khan. The police chief of New York City, Ray Kelly, said Khan was the publisher of Al-Qaeda's English-language magazine "Inspire."

In Washington, Obama said "the death of Awlaqi is a major blow to Al-Qaeda's most active operational affiliate" and "marks another significant milestone in the broader effort to defeat Al-Qaeda and its affiliates."

He said that while the organisation was weakened, it was still dangerous, and the United States would remain vigilant.

Al-Qaeda's Yemen branch issued a new claim of deadly attacks dated on the same day Awlaqi was killed.

In the statement received by AFP in the main southern Yemeni city Aden, Al-Qaeda in the Arabian Peninsula claimed a series of attacks in the south but made no mention of Awlaqi's death.

AQAP said it had killed 130 Yemeni troops in an attack on a garrison in the Abyan provincial capital Zinjibar, east of Aden, on September 14.

It said it had killed two Yemeni soldiers in an attack on September 11 and 10 in another the following day.

Tribal sources told AFP Awlaqi was killed in what was probably an American air strike on two vehicles in Marib. CNN and The Washington Post reported that a CIA drone had carried out the strike.

In April 2010, a US official said the Obama administration had authorised the targeted killing of Awlaqi after intelligence agencies concluded he was directly involved in anti-US plots.

The White House, however, dodged questions over the circumstances surrounding the killing.

US Defense Secretary Leon Panetta, while refusing to confirm any US action or offer operational details, thanked the Yemenis for their "assistance."

"We've been working with the Yemenis over a long period of time to be able to target Awlaqi and I want to congratulate them on their efforts, their intelligence assistance, their operational assistance to get this job done," he said.

One of the tribal sources quoted a man wounded in the strike, Khamis Saleh Arfaj, as saying he was hosting the group at his house when the attack occurred.

He said they were seated on the ground outside eating a meal when a first strike hit.

The men rushed to their vehicles to flee, and the lead vehicle, with Awlaqi aboard, was destroyed in a second strike.

Arfaj, who was following in a second vehicle and was lightly wounded, said Awlaqi and Arfaj's brother Salem "were killed instantly from a direct missile hit to their pick-up" truck.

He said the others killed were Samir Khan, two unnamed Saudis and a local tribesman, and a man named Mohammed Mosen al-Naaj.

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

"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 travelling in."

Earlier this month, The Washington Post said the United States was building an array of secret new drone bases to strike Al-Qaeda targets in Yemen and Somalia.

Yemeni authorities officially deny the use of drones in their country, saying Washington provides only logistical support to Sanaa's fight against extremists.

Obama said Awlaqi was the leader of external operations of Al-Qaeda in the Arabian Peninsula (AQAP) and had taken the lead in planning and directing efforts to murder innocent Americans.

His killing was a tribute to the US intelligence community and to Yemen's cooperation with the United States in a common anti-terror campaign, Obama said, while warning that, though "weakened," AQAP is still "dangerous."

"Going forward, we will remain vigilant against any threats to the United States or our allies and partners," said Obama.

"But make no mistake, this is further proof that Al-Qaeda and its affiliates will find no safe haven anywhere in the world."

White House spokesman Jay Carney declined to answer tough questions about the killing, as a debate raged over Awlaqi's rights as an American citizen.

"I'm not going to talk about the circumstances of Awlaqi's death. And I'm not going to acknowledge or concede or accept premises embedded in questions," Carney said.

Civil rights groups raised red flags, with some arguing it would be illegal for the US military to kill an American citizen on the battlefield, following no attempt to indict him.

Last year, civil liberties groups filed a lawsuit on behalf of the cleric's father, Nasser al-Awlaqi, saying it was unconstitutional for the CIA to order the death of an American citizen without due process.

A judge dismissed the case without ruling on its merit, but said it raised serious constitutional issues.

On Capitol Hill, there was bipartisan satisfaction with Awlaqi's death.

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-Qaeda and its affiliates."

The top Democrat on the House Armed Services Committee, Adam Smith, said Awlaqi "will no longer be able to propagate hatred and manipulate impressionable youth to take up arms against the United States and our allies."