WASHINGTON - American forces killed the leader of extremist Shebab militants in Somalia in a bombing raid this week, US officials announced Friday, calling it a serious blow to Al-Qaeda's terror network.

The fatal strike against Ahmed Abdi Godane embodied President Barack Obama's approach to fighting Al-Qaeda and its allies, preferring to take out key figures from the air rather than deploying large numbers of troops on the ground.

"We have confirmed that Ahmed Godane, the co-founder of al-Shebab, has been killed" in an air raid carried out on Monday, Pentagon press secretary Rear Admiral John Kirby said.

Godane's death is "a major symbolic and operational loss to the largest Al-Qaeda affiliate in Africa and reflects years of painstaking work by our intelligence, military and law enforcement professionals," the White House said in a statement.

The air attack was launched at 1520 GMT on Monday, with both drones and manned aircraft bombing a gathering of Shebab commanders with Hellfire missiles and laser-guided bombs, officials had said earlier this week.

But even as Al-Qaeda suffered another setback, Washington and its Western allies now face a mounting challenge from a separate extremist organization - the jihadists of Islamic State (IS) - who have seized territory across Syria and Iraq with brutal tactics.

US officials did not specify how Godane's death was confirmed, but in similar operations in the past, US intelligence agencies have tested DNA samples and backed it up with information gleaned from eavesdropping.

The State Department has listed Godane as one of the world's eight top terror fugitives and analysts say his death marks a crippling setback for the Shebab forces.

Godane, 37, who reportedly trained in Afghanistan with the Taliban, took over the leadership of the Shebab in 2008 after then chief Adan Hashi Ayro was killed by a US missile strike.

Godane had overseen the group's transformation from local insurgency to major regional guerrilla threat, after eliminating his rivals inside the organization.

Under pressure in Somalia from African Union forces and having lost control of key towns in the past three years, Godane had shifted the group's focus from a previous mainly nationalist agenda to one espousing global jihad.

Godane has boasted that Shebab gunmen carried out the 2013 attack on the Westgate shopping mall in Nairobi, which left at least 67 shoppers, staff and security personnel dead.

US officials vowed to keep up pressure on Shebab, which under Godane had forged an alliance with Al-Qaeda.

Although the strike was "an important step forward" in the campaign against Shebab extremists, the United States "will continue to use the tools at our disposal - financial, diplomatic, intelligence and military - to address the threat that al-Shebab and other terrorist groups pose to the United States and the American people," the White House said.

"We will also continue to support our international partners, particularly the African Union Mission in Somalia, that are working to support the Federal Government of Somalia build a secure and stable future for the Somali people," it said.

Shebab militants are fighting to overthrow the Somali government, regularly launching attacks against state targets and in neighbouring countries that contribute to the African Union force there.

Monday's US air strike came days after AU troops and government forces launched "Operation Indian Ocean", a major offensive aimed at seizing key ports from the Islamist rebels.

Last October, US special operations forces launched an attack on a house in Barawe against another top Shebab commander but were forced to withdraw without killing their target. - AFP