The weekend seizure of a Nairobi, Kenya, shopping mall by Somalia-based jihadists linked to al-Qaida, slaughtering dozens of people, underlines how, two years after the Americans assassinated Osama bin Laden, jihadists are widening their offensive across Africa as well as the Arab world.

U.S. officials have boasted in recent weeks that al-Qaida is on the run, its core leadership in Pakistan hammered by drone attacks.

But Saturday's takeover of the landmark Westgate mall in Kenya's capital, by 10-15 fighters of the al-Shabaab movement in neighboring Somalia, widely written off after a series of military setbacks and a brutal internal power struggle, demonstrates that the group's hardliners are still a force to be reckoned with.

Al-Shabaab claimed responsibility for the ferocious killing spree in downtown Nairobi.

It claimed it was retaliation for Kenyan participation in an 18,000-strong U.S.-backed African Union military intervention in Somalia in 2011-12 that drove the jihadists out of Mogadishu, Somalia's war-scarred capital, and other important urban bases, including their economic hub in the southern port of Kismayo.

The attack in Nairobi by a group that a Twitter account linked to al-Shabaab allegedly including five Americans, a Canadian, two Swedes and a Briton, was unleashed simultaneously with an assault on African Union peacekeepers in Mogadishu, U.S. officials say.

The Nairobi operation had the look of a suicide mission by a die-hard group, cornered by Kenyan security forces with an unknown number of hostages in the upper floors of the four-story mall after killing dozens of non-Muslims, prepared to shoot it out to the last man and inflict the maximum number of casualties.

It's not clear whether the gunmen had infiltrated from Somalia or belong to a sleeper cell established in the city by al-Shabaab's hard-line leader, Ahmed Abdi Godane, who appears to have won the internal power struggle that was ignited by its recent military defeats.

U.S., British and Kenyan intelligence officials have warned for months that Godane was recruiting significant numbers of foreigners who would attract less suspicion in Kenya than Somali natives.

Al-Shabaab has always been pretty loose-knit, and some analysts had suggested the factional split spelled the end of the group as a major player in the Horn of Africa where Western powers and African Union countries have sought for two decades to end anarchy and clan warfare that followed the 1991 otherthrow of military dictator Mohamed Siad Barre.

The power struggle, which got pretty messy, was between the nationalist faction, which seeks to fight foreign intervention, and the transational jihadists led by Godane, aka Mukhtar Abu Zubayr, who see the struggle as part of a global jihad. It was he who decided in 2011 to affiliate with al-Qaida.

Godane and his globalists, who include scores of American, European and other foreigner volunteers, consolidated his power in an internal coup in June.

He executed four rival commanders, two of whom, identified as al-Afghani and Burhan, were co-founders of al-Shabaab.

The group's spiritual leader, Sheikh Hassan Dahir Aweys, leader of a powerful clan that has in the past dallied with both al-Shabaab and the Western-backed Transitional Federal Government, fled for his life.

He was reported to have been captured by government forces, but some insiders say he defected to save his skin.

Two key victims of the internal rivalries ware Alabama-born commander Omar Hammami, known as Abu Mansoor al-Amriki, and a British citizen known as Usama al-Britani.

They were shot dead Sept. 12 in a dawn ambush by Godane's people. Hammami, who was on the U.S. most wanted list, had been highly critical of Godane for some time and accused him of being a dictator. Godane had earlier slain several of Hammami's associates.

"The apparent decision by Godane and his fellow hard-liners to again take the fight beyond Somalia's borders looks like a bid to regain the initiative in the face of these setbacks and disagreements," international affairs commentator Simon Tisdall observed in The Guardian newspaper of London

"In addition, the group's occasional bomb attacks in Mogadishu keep the government on the back foot."

Al-Shabaab has attacked the TFG's African allies before. Godane ordered bombings in Uganda, another TFG ally, July 11, 2010, that killed 76 people.

There have been dozens of grenade attacks in Kenya in recent months and authorities in Nairobi say they thwarted a major jihadist multiple bombing operation several weeks ago.