A Kenyan official says police seized material they believe can be used to assemble a bomb, a day after the US gave warning of an imminent terrorist attack in Kenya.

A police official, who asked for anonymity because he is not authorised to speak to the press, said on Saturday that three suspects dropped a bag and ran after police confronted them near a highly populated slum.

The official says police found 6kg of ammonium nitrate and other items they believe can be used to make a bomb.

Police said an improvised bomb killed one person and injured 32 others in Nairobi's business district last month. Officials believe ammonium nitrate was used to assemble that bomb.

Somalia's al-Shabab, believed by the US administration to be linked to al-Qaeda, has threatened to retaliate after Kenya sent troops to Somalia to pursue its fighters.

Source: Agencies