A car bomb exploded outside the main gate of a police station in the Nairobi on Wednesday, killing four people including two police officers, according to the Interior Ministry.
The incident happened after police in the Kenyan capital had stopped what they believed was a suspicious car at a set of traffic lights in Pangani. As they took the occupants in to be questioned, the car exploded.
A second controlled detonation was carried out by bomb disposal officers shortly after the initial blast, a Reuters witness said.
It was not immediately clear who was behind the attack.
Pangani is located next to Nairobi's Eastleigh district - an area targeted in past bomb and grenade attacks that police say Somali militants and their sympathisers are responsible for.
Since the attack on Westgate Mall in September 2013 where 67 people died, terror warnings have been constant in Kenya.
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 after the country’s troops moved into southern Somalia in 2011.
Patrick Kimiti was close to the car when it exploded. "I was just tossed up immediately and when I landed, I lay on the ground. There was so much dust.
"People were screaming. Cars were skidding and making U-turns," he said.
Additional reporting by agencies