A Kenyan lawmaker was gunned down on a busy Nairobi street by a motorcycle-riding assassin on Wednesday evening, in what the police described as a “targeted and premeditated” attack.

The lawmaker, Charles Were, who was serving a second term in Parliament, was in a vehicle stopped at a traffic light when he was killed, the police said. Witnesses reported that a person riding on the back of a motorcycle had hopped off and shot into the passenger side of Mr. Were’s car before being whisked away by the motorcycle’s driver, the police said.

A motive was not immediately clear. Muchiri Nyaga, a police spokesman, said in a statement on Wednesday that it was too early for the authorities to provide additional details.