At least five people were killed and 18 others seriously injured in a grenade attack in Nairobi's Eastleigh residential estate mainly inhabited by Kenyans of Somali origin.

Regional police commander Moses Ombati confirmed the incident which he said occurred after an explosion was detonated on a public passenger vehicle with 25-seater capacity.

"I can confirm that five people were killed while 18 others were seriously injured in the explosion on a mini-bus at St. Teresa Church in Eastleigh. Among the dead include three men and two women," Ombati told Xinhua by telephone.

He said the vehicle was extensively damaged in the explosion which he suspected was planted. "We have launched investigations to establish the cause of the blast but so far we have not arrested any suspect," Ombati said.

Eye witnesses said there is tension in the area as most of the businessmen have closed their shops for fear of looting and fighting.

"There is a lot of tension hear at Fourth Avenue in Eastleigh. Some people are fighting while business people have closed their shops. There is total confusion in Eastleigh," Mohammed Hussein who resides in the estate told Xinhua by telephone.

The Eastleigh residential estate has experienced a spate of grenade attacks in the recent past blamed on sympathizers of Al- Shabaab who are living in Nairobi.

The police have appealed to Kenyans to be extra alert and to take positively the heightened security measures being undertaken by the police in Nairobi.

The incident comes as the police have intensified security in all hotels, key buildings and restaurants, particularly along the border with neighboring Somalia where Al-Qaida-linked fighters are waging an insurgency to avert reprisals.

Kenya blames Al-Shabaab for the kidnappings of foreigners, and fears its tourist and business economy will be destroyed if it allows the insurgents to go on unchallenged.

The grenade and landmine explosions come as the biggest warning to Kenya so far that the insurgents are keen to orchestrate devastating terror attacks in the country after the capture of their strategic port city of Kismayo which served as the revenue collection center.

The trend of the attacks particularly in northern Kenya, Nairobi and Mombasa which seemingly are well coordinated since several suspects have been arrested, has heightened worries among Kenyans.