Kenyan troops were officially integrated into the African Union's peacekeeping mission in Somalia (AMISOM), with Kenya's defense minister signing an agreement at AU headquarters Saturday.

"We conclude the process of establishing a formal, legal framework for the integration of the Kenyan defense forces into AMISOM," Minister of Defense Yusuf Haji said at the signing in Addis Ababa, the Ethiopian capital.

Several people were wounded in a large blast in the center of the Kenyan capital Nairobi Monday, although the cause of the explosion was not known, an Agence France Presse reporter at the scene said.

Kenya has been hit by a wave of grenade attacks the police have repeatedly blamed on Somalia's al-Qaida linked Shebab insurgents or its supporters.

At least 50 people have died as a result of heavy rains lashing Kenya since March, the country's Red Cross said Saturday.

In the latest incident on Friday night, seven people drowned about 20 kilometers southwest of Nairobi as rains swept the capital and its surrounding region, it said.

A grenade set off by a worshipper in a Nairobi church killed one person on Sunday and injured at least 10 others, police in the Kenyan capital said.

"We have one fatality, and there are more than 10 others who have been injured," area deputy police Chief Joseph Gichangi said.

The U.S. embassy in Kenya warned Monday of a possible attack which is "in the last stages of planning" on Nairobi hotels and key government buildings and urged American citizens to be cautious.

"Timing of the attack is not known, however, the embassy has reason to believe that the potential attack is in the last stages of planning," the embassy said in a statement.

Kenyan rangers shot dead five suspected elephant poachers in a night-time firefight in the north of the country, the Kenya Wildlife Service (KWS) said on Saturday.

"Five suspected poachers were last night gunned down and one escaped during a fierce exchange of fire with Kenya Wildlife Service rangers at Chepareria in West Pokot County," it said.

At least one person was killed and 14 others were wounded in explosions in a restaurant in the Kenyan city of Mombasa and in the nearby town of Mtwapa, police said.

Police said one of 12 people injured in what appeared to be a grenade attack in Mtwapa died from his injuries on his way to or on arrival at hospital. Coast province police chief Aggrey Adoli said that a second grenade "hurled at a restaurant in Mombasa" injured three, including one police officer.

Mali's coup leader Captain Amadou Sanogo has pledged the safe release of three top African foreign officials stranded in Bamako after the putsch, an African Union source said Saturday.

AU Commission chief Jean Ping spoke to Sanogo on the phone on Friday and was assured the foreign ministers of Kenya and Zimbabwe, as well as a Tunisian secretary of state in charge of Arab and African affairs would return safely.

Kenyan police said Monday they have arrested four people in connection with grenade attacks that killed six people in Nairobi, which Kenya blames on supporters of Somali Shebab insurgents.

"On the Al-Shebab threats and attacks at the Machakos bus terminus, four highly suspected criminals were arrested and are undergoing intensive interrogation," Nairobi Provincial Police chief Antony Kibuchi said.

Kenya faced a new terror threat on Sunday after a grenade attack blamed on Somali Islamist militia killed six people and injured 63 in a bus terminal in the capital Nairobi.

Four grenades were thrown Saturday night only yards apart from a car driving past the busy terminal, Internal Security Minister George Saitoti said Sunday.