WASHINGTON — US President Barack Obama warned Africans that groups like Al-Qaeda saw their "innocent" lives as cheap, in a personal challenge to extremists on the continent after the Uganda bombings.

A US official meanwhile branded Al-Qaeda, linked to the Somalia-based Shebab group which claimed the attacks, as "racist," as the United States cranked up its diplomatic response to increasingly active extremists in Africa.

Obama, leveraging his African heritage and popularity on the continent, took direct aim at the Shebab and Al-Qaeda after attacks on crowds in Kampala glued to the World Cup final on Sunday killed at least 76 people.

"What you?ve seen in some of the statements that have been made by these terrorist organizations is that they do not regard African life as valuable in and of itself," Obama told the South African Broadcasting Corporation (SABC).

"They see it as a potential place where you can carry out ideological battles that kill innocents without regard to long-term consequences for their short-term tactical gains," he said, in the interview to be broadcast early Wednesday.

Obama's intervention marked the first, direct comments by the president, whose father was Kenyan, on the Kampala bombings.

A senior American official made clear Obama was taking a direct swipe at the ideology and motives of Al-Qaeda affiliates on the continent, which US intelligence agencies say are the extremist group's most active franchises.

"The president references the fact that both US intelligence and past Al-Qaeda actions make clear that Al-Qaeda and the groups like (Shebab) that they inspire -- do not value African life.

"In short, Al-Qaeda is a racist organization that treats black Africans like cannon fodder and does not value human life," the official said, on condition of anonymity.

US officials drew parallels between the Uganda attacks and the 1998 bombings of American embassies in Kenya and Tanzania, which killed hundreds of Africans, to suggest Al-Qaeda viewed people on the continent as acceptable casualties of its wider goals.

A senior US official also said that US intelligence analysts had concluded that Al-Qaeda leadership figures had specifically targeted black Africans to become suicide bombers.

They did so, the official said in the belief that social and economic conditions on the continent made them more susceptible to recruitment.

Earlier, a separate administration official validated the Shebab's claims to have carried out the bombing, and expressed fears the group could seek to carry out attacks outside of Africa.

The official, also speaking on condition of anonymity, said that though the United States had tracked the rebel group and knew about its Al-Qaeda links, it had no forewarning of the strikes in Kampala.

"At this point, there are indications that (Shebab) was indeed responsible for it and that its claiming responsibility is real," the official told reporters.

The official added that it was known that a number of Americans had gone to Somalia to link up with the group, which has threatened US interests, but said law enforcement agencies here were aware of the potential threat.

"We're very vigilant for any indication of individuals from Somalia coming here to the United States to engage in these types of extremist and terrorist activities," the official said.

But in the wake of the thwarted attack on a US airliner last year by a young Nigerian man allegedly trained by Al-Qaeda in Yemen, he did warn the group had now demonstrated it had the capacity, and willingness to look outside Somalia.

"I'm worried about any organization, particularly any one that is associated with Al-Qaeda and has Al-Qaeda elements sprinkled within it, and their determination as well as potential capability to carry out an attack outside of the region.

"There are ways that they can carry out relatively unsophisticated attacks but still with very lethal results."

Obama also dwelt in the SABC interview on the cruel timing of the attacks.

"It was so tragic and ironic to see an explosion like this take place when people in Africa were celebrating and watching the World Cup take place in South Africa," he said in excerpts released by the White House.

"On the one hand, you have a vision of an Africa on the move, an Africa that is unified, an Africa that is modernizing and creating opportunities.

"On the other hand, you?ve got a vision of Al-Qaeda and (Shebab) that is about destruction and death.

Shebab insurgents said the blasts that ripped through a crowded bar and a restaurant in Kampala on Sunday were retaliation for the presence of Ugandan troops in Mogadishu.

They were the first ever attack by the Shebab outside Somalia, marking an unprecedented internationalization of Somalia's 20-year-old civil war.