The group continues to make cross-border raids to pressure Kenya to withdraw its forces from the AU peacekeeping mission in Somalia.
Al-Shabab fighters have attacked a police vehicle in eastern Kenya, killing two officers and one civilian, police and the armed group said.
The truck was travelling from Hayley Lapsset camp to Garissa town, about 120km (75 miles) from the Somali border, when it hit an explosive device, according to a police statement on Wednesday.
The fighters then fired a rocket-propelled grenade at the vehicle and engaged in a heavy firefight which killed the victims, police said.
Al-Shabab’s Radio Andalus said in a broadcast their gunmen killed two Kenyan security force members and injured several others in the attack.
The group killed 166 people at Garissa University in 2015, and 67 at a mall in Nairobi in 2013, but the frequency and severity of al-Shabab attacks in Kenya have reduced in recent years.
The al-Qaeda-linked group continues to make cross-border raids to pressure Kenya into withdrawing its forces from the African Union-mandated peacekeeping force in Somalia.
Images shared by police showed a burned-out truck and a body lying in the sand. Police said they had little information on the whereabouts of other police officers travelling in the vehicle.
Al-Shabab has been under pressure in Somalia since August when President Hassan Sheikh Mohamud began an offensive against them, supported by the United States, the African Union Transition Mission in Somalia (ATMIS) and allied local militias.