Kenyan officials say Somali militants have killed 12 people, including three police reservists, in a border ambush. A spokesman for the militant group al-Shabab claimed responsibility for Monday's attack in northeast Kenya near its border with Somalia. David Kimaiyo, Kenya's top police chief, said the attack began when bandits shot at four vehicles transporting khat, a chewed stimulant popular throughout the region. He said police officers who responded to the attack drove into an ambush. The National Disaster Operation Center said two police vehicles were destroyed. Security fears are running high in Kenya because of al-Shabab's threat to attack Kenyan cities. The United States, Britain, Australia and France all have issued security warnings to its citizens in Kenya in recent days.