A grenade attack on a Nairobi bus station on Saturday killed at least four people and wounded nearly 60 others, in an assault Kenyan police blamed on the Islamist Shebab militia.

A hospital spokesman said at least eight people were in a critical condition following the attack, during which witnesses reported seeing grenades thrown from a car.

Kenya's army said Saturday that four months of military strikes on Shebab rebels in southern Somalia have weakened the Al-Qaida-linked insurgents and have disrupted their sources of revenue.

Air strikes and ground raids had cut off Shebab's trade routes and drove them from key towns where they conducted business, said military information and operations officer Colonel Cyrus Oguna.

A Kenyan aid worker and his Pakistani driver working for an international charity are missing, feared abducted in southern Pakistan, police said Monday.

Police official Saqib Ismail said the Kenyan works for Care International and that his car was found abandoned in the town of Naushahro Feroz on Sunday. Since then, there has been no news of about the men's whereabouts.

Kenyan troops clashed with Somalia's al-Qaida linked Shebab militants in southern Somalia, the latest attack in a three-month long push forward against insurgent bases, officials said Monday.

Two Kenyan and one Somali soldiers were killed during an attack late Sunday on hardline Shehab positions at Delbio and Hosingo, said Kenyan army spokesman Major Emmanuel Chirchir, who claimed Shebab gunmen had retreated.

Kenyan police have arrested 29 Ugandans suspected of seeking to join Islamist rebels in Somalia, a police spokesman said Sunday.

The suspects were arrested in Nairobi and were "undergoing interrogation," Eric Kiraithe told AFP. "Police are investigating them because they are believed to have been headed to Somalia to fight" alongside Shebab rebels.

Gunmen killed six Kenyans including four policemen in the latest of a string of attacks in the northeastern border region with war-torn Somalia, police said Thursday.

Two other policemen were wounded in the attack some 100 kilometers (60 miles) from Somalia -- an area hit by a series of blasts in the three months since Nairobi sent troops into Somalia to fight Islamist Shebab insurgents.

Kenya admitted Saturday the threat from al-Qaida-linked Shebab insurgents from neighboring Somalia was not "totally neutralized," as Britain warned its nationals of a heightened risk of attack.

The British Foreign Office said it believed there was a heightened threat of "terrorist attacks" in the Kenyan capital and that attacks "may be in the final stages of planning."

Britain said Saturday it believed there was a heightened threat of "terrorist attacks" in the Kenyan capital Nairobi and that attacks "may be in the final stages of planning".

"The Kenyan authorities have alerted the public to a heightened threat from terrorist attacks in Nairobi. We believe that terrorists may be in the final stages of planning attacks," a Foreign Office statement said.

Kenyan fighter jets killed at least 60 Islamist Shebab insurgents in southern Somalia in the latest air strike on insurgent positions, officials said Saturday.

"Levels of casualties were very high in air strikes on Friday," Kenyan army spokesman Colonel Cyrus Oguna told reporters, adding the bombing raids hit rebel positions in Garbahare in southern Somalia's Gedo region.

Five people were killed in a New Year's Eve hand grenade attack and shooting in a bar in the eastern Kenyan town of Garissa near the border with Somalia, police said Sunday.

"There was an explosion in a club in town shortly before midnight (Saturday) and five people died," a senior police officer at Northeast provincial headquarters told AFP.