Updated

Police in Nairobi say a car bomb has exploded outside a police station in central Nairobi and killed four people.

David Kimaiya, the inspector general of police, says two officers are among the dead from Wednesday night's explosion.

An Associated Press reporter at the scene said it appeared that the blast ripped apart the back end of a sedan. The blast happened near a police station's main gate.

Terror warnings have been a constant in Kenya in recent months, particularly after September's attack on Westgate Mall killed at least 67 people.

Most of the small-scale attacks and explosions are blamed on al-Shabab, the militant group in Somalia that has vowed revenge attacks in Kenya because Kenyan troops moved into southern Somalia in 2011.