NAIROBI, Kenya (AP) — A man was shot dead after stabbing a policeman guarding the perimeter wall of the US Embassy in Nairobi and trying to take his gun, a Kenyan police official said Thursday.

The policeman who had been stabbed opened fire in self-defence and killed the attacker, said Vitalis Otieno, the officer in charge of the Gigiri area that hosts several embassies and the UN’s African headquarters.

“He fired first and shot the person and the person died on the spot,” Otieno said.

The identity of the attacker, a Kenyan from the volatile region of Wajir near Somalia, is known to police, Otieno said.

Federal Bureau of Investigation personnel were seen collecting evidence at the scene of the shooting.

The US Embassy confirmed there was a shooting and said no embassy personnel were involved.

Wajir county has been cited by Kenyan authorities as a hot-spot for recruitment by the Islamic extremist group al-Shabab from neighbouring Somalia.

Al-Shabab has vowed retribution on Kenya for sending troops to Somalia to fight the militants. The group has carried out a wave of attacks in Kenya that have left hundreds dead.

The extremist group claimed responsibility for an attack Tuesday in Mandera county that killed 12 people, saying its fighters were targeting Christians.

Al-Shabab is al-Qaida’s affiliate in the region, and it hosted Fazul Abdallah Mohammed, who was accused of masterminding the US Embassy bombings in Kenya and Tanzania in 1998 that killed over 200 people. Mohammed was shot dead by Somali troops in 2011.

Recently, Kenya has been battling the recruitment of youth by the Islamic State group, which is al-Qaida’s rival. Kenyan police have linked three women who were killed after they allegedly attacked a police station in Mombasa to the Islamic State.