A grenade was thrown into a discotheque in the Kenyan capital Nairobi early Monday injuring 14 people, all Kenyans, in an attack police linked with recent threats made by Somali Shebab insurgents.

"Yes, we are linking the grenade attack to the threats that have been issued by Shebab and that is why I am appealing to city residents to be vigilant and cooperate with our officers," Antony Kibuchi, provincial police chief for Nairobi, said.

The U.S. embassy in Nairobi warned Americans on Saturday of an "imminent threat" of attacks possibly targeting foreigners, one week after Kenyan forces crossed into Somalia to hunt down Shebab fighters.

The embassy cited "credible information of an imminent threat of terrorist attacks directed at prominent Kenyan facilities and areas where foreigners are known to congregate, such as malls and night clubs."

African Union and Somali government troops battled Shebab rebels in the anarchic capital Mogadishu Thursday, as Kenyan troops in the south continued their assault on Islamist positions there.

Heavy fighting broke out before dawn in Mogadishu as AU-backed Somali forces advanced on holdout Islamist Shebab positions, officials and witnesses said.

Kenyan jets struck Shebab positions in Somalia Wednesday in a bid to rid the border area of Islamist rebels they blame for a spate of abductions, including that of a French woman who died in captivity.

Kenyan ground troops guided by pro-government Somali forces prepared for a fresh assault against the insurgents with the blessing of the Western-backed government in Mogadishu and its Ugandan protectors.

The search for the world's first malaria vaccine received a boost with the release of early results from a major clinical trial showing it cut risk by about half in African children.

The vaccine known as RTS,S is made by the British pharmaceutical giant GlaxoSmithKline's lab in Belgium, and is the first of its kind to attempt to block a parasite, rather than bacteria or viruses.

A handicapped Frenchwoman who was kidnapped from her beachfront home at a Kenyan resort island and taken to neighboring Somalia has died, France said on Wednesday.

"The contacts through which the French government was seeking to obtain the release of Marie Dedieu, held in Somalia since October 1, have announced her death, but we have not been able to determine the date nor the circumstances," the foreign ministry said in a statement.

Kenyan troops using aerial cover advanced Tuesday on a strategic rebel-held Somali town, even as Nairobi police stepped up security for fear of reprisal attacks by Islamists.

"Our forces will be concentrating on operations in Afmadow region today, they started moving there late on Monday," said Kenyan army spokesman Major Emmanuel Chirchir.

Two Britons have been arrested in Kenya near the border with Somalia, police in Wales said Tuesday.

The pair, believed to be from the Welsh capital Cardiff, were detained on Sunday, according to the Foreign Office in London, which said it was ready to provide consular assistance if required.

Kenyan troops have crossed the border into war-torn Somalia to attack Islamist Shebab rebels they accuse of being behind several recent kidnappings of foreigners, Kenyan officials said Sunday.

"We have crossed into Somalia in pursuit of the Shehab, who are responsible for the kidnappings and attacks on our country," government spokesman Alfred Matua told AFP.

Somali Islamist Shebab rebels on Thursday kidnapped two female Spanish aid workers from Kenya's Dadaab refugee camp, a regional police official said.

"Two aid workers of Spanish nationality have been kidnapped by the Shebab, they are working for MSF (Medecins Sans Frontieres)," Leo Nyongesa, regional police chief, told AFP.