A former Guantanamo Bay detainee was killed by a US airstrike on Yemen, as an American bombing campaign targeting one of al Qaeda's strongest branches struck more targets in the country over a week than it had in any previous year.

Yasir al-Silmi died alongside, Usayd al-Adnani, an emir with al Qaeda in the Arabic Peninsula (AQAP) within the Abyan governorate, the Pentagon said.

Mr al-Silmi, a Yemeni citizen, spent several months in extrajudicial detainment at the Cuban naval base after being apprehended in Pakistan. But he was repatriated to his homeland in 2009.

"More than 20 strikes targeted AQAP militants, equipment and infrastructure," said Pentagon Spokesman, Captain Jeff Davis.

The situation in Yemen Show all 14 1 /14 The situation in Yemen The situation in Yemen Houthi supporters trample on a US flag during a gathering mobilizing more fighters into several Yemeni battlefronts, in Sana'a, Yemen EPA The situation in Yemen People carry the coffins of men, who were killed in the recent Saudi-led airstrikes during their funeral, in the Old City of Sanaa, Yemen AP The situation in Yemen Pro-government fighters give food to Yemeni children on the road leading to the southwestern port city of Mokha. Yemeni rebels are putting up fierce resistance in a key Red Sea port city where they are encircled by pro-government force Getty Images The situation in Yemen A Yemeni stands in front of a graffiti protesting US military operations in war-affected Yemen, in Sana'a, Yemen. According to reports, US Special Forces troops allegedly disembarked from US helicopters in the Yemeni town of Yakla and attacked several houses belonging to members of the terrorist group Al-Qaeda, killing three high-ranking Al-Qaeda members and nine civilians, six women and three children. One American serviceman has been killed and three injured in the attack EPA The situation in Yemen US Special Forces troops allegedly disembarked from US helicopters in the Yemeni town of Yakla and attacked several houses belonging to members of the terrorist group Al-Qaeda, killing three high-ranking Al-Qaeda members and nine civilians, six women and three children. One American serviceman has been killed and three injured in the attack EPA The situation in Yemen A Yemeni female fighter supporting the Shiite Huthi rebels, and carrying weapons used for ceremonial purposes, takes part in an anti-Saudi rally in the capital Sanaa Getty Images The situation in Yemen Yemeni female fighters supporting the Shiite Huthi rebels, and carrying weapons used for ceremonial purposes, take part in an anti-Saudi rally in the capital Sanaa Getty Images The situation in Yemen A boy shouts slogans next to pro-Houthi fighters, who have been injured during recent fighting, during a rally held to honour those injured or maimed while fighting in Houthi ranks in Sanaa, Yemen Reuters The situation in Yemen Balls of fire and smoke rise from a Houthi-held military camp following alleged Saudi-led airstrikes, in Sana'a, Yemen EPA The situation in Yemen Yemenis search under the rubble of damaged houses following reported Saudi-led coalition air strikes on the outskirts of the Yemeni capital Sanaa Getty Images The situation in Yemen A Yemeni boy looks on as Yemenis search under the rubble of damaged houses following reported Saudi-led coalition air strikes on the outskirts of the Yemeni capital Sanaa Getty The situation in Yemen A Yemeni boy sits amidst the rubble of damaged houses following reported Saudi-led coalition air strikes on the outskirts of the Yemeni capital Sanaa AFP/Getty The situation in Yemen Marine One with US President Donald Trump flies with a decoy and support helicopters to Dover Air Force Base in Dover, Delaware, for the dignified transfer of Navy Seal Chief Petty Officer William 'Ryan' Owens who was killed in Yemen Getty Images The situation in Yemen US President Donald Trump aboard the Marine One to greet the remains of a US military commando killed during a raid on the al Qaeda militant group in southern Yemen on Sunday, at Dover Air Force Base, Delaware, US Reuters

He added that they would "degrade the AQAP's ability to coordinate external terror attacks and limit their ability to use territory seized from the legitimate government of Yemen as a safe space for terror plotting."

He said: "Targets of the strikes included militants, equipment, infrastructure, heavy weapons systems and fighting positions."

The strikes follow a January raid in which 30 Yemeni civilians lost their lives, including 10 women and children, as helicopter gunships bombed militants as they fought with US Navy Seals.

The US considers the group, also known as Ansar al-Sharia, to be the most active and dangerous of the various Al-Qaeda splinter organisations.

Although it has not yet launched any successful attacks in the West, AQAP is responsible for the deadliest terror attack in Yemeni history, killing 120 military personnel with a suicide bomb in 2012.

The civil war pitting rebels led by the Houthi Shiites against a Sunni coalition government backed by Saudi Arabia and the United States has enabled AQAP to seize significant swathes of territory.

For some time it had control of the strategic port city of Mukalla and reportedly seized some $120 million from the city's bank.

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American Special Forces helped oust AQAP from Mukalla in 2016, but the group remains the most powerful third party in the conflict.

The US' main involvement in the war has been supplying bombs to the Saudi-led coalition, although it has also fired directly on the opposition, who are demanding more political power and autonomy for the Shiite religious autonomy.

Over 10,000 people have died in the conflict, including 4000 civilians. US-made bombs have repeatedly been used to kill civilians in unlawful airstrikes against Yemeni citizens, according to Human Rights Watch (HRW).

The organisation said it was an American bomb which killed 140 people, mainly civilians, in a highly-publicised airstrike on a Houthi funeral last year.

The US approved more than US$20 billion in military sales to Saudi Arabia in 2015 alone, even as the powerful Gulf state has been accused of "deliberately targeting impoverished Yemen’s farms and agricultural industry", by HRW.

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America is now stepping up its own attacks on AQAP, hitting over 40 targets in the last seven days – more than in any previous year.

Pentagon spokesperson Captain Jeff Davies said the group had "taken advantage of ungoverned spaces in Yemen to plot, direct and inspire terror attacks against the United States and our allies."