NAIROBI - At least three people were injured, two critically, in an explosion in a residential estate in Nairobi Tuesday.

Divisional police commander Hassan Burua said unidentified "thugs" had planted an improvised explosive device on First Avenue in Eastleigh estate, which is mainly inhabited by Kenyans of Somali origin.

"We have confirmed three people were injured. Two are in critical condition and have been rushed to the hospital. One was treated and discharged," Burua told reporters at the scene of the incident.

Some roads have been blocked in the Kenyan capital as anti-terrorism police analyze the blast scene.

"We have launched investigations to probe into the motive behind the attack and a major manhunt for those responsible is underway," Barua said.

The incident came as the police have intensified security in all hotels, key buildings and restaurants in Kenya, particularly along the border with neighboring Somalia, where al-Qaida-linked militants are waging an insurgency against a Kenyan military campaign.