Updated

Gunmen suspected to be al-Shabab Islamic extremists killed an administrative chief in an attack in Kenya's north that left two police reservists missing, an official said Tuesday.

The attack took place in Omar Jillo in Mandera county on Monday night, Regional Coordinator Mohamud Saleh said. The county borders Somalia, where al-Shabab is based. Omar Jillo is among several towns in the area under dusk-to-dawn curfew over insecurity caused by the al-Qaida-linked extremists.

A police report seen by The Associated Press says four unknown men believed to be al-Shabab members broke into the compound of administrative chief Dekow Abbey Sirat and interrogated him before they shot him dead.

Mandera has been hardest hit in recent years by an al-Shabab campaign to avenge Kenyan troop presence in Somalia since 2011. Kenya's troops are part of the African Union force in Somalia helping the fragile central government counter al-Shabab's insurgency.

On Friday, suspected al-Shabab extremists killed two quarry workers in Mandera. It was the third attack on quarry workers, the majority of whom are not Muslim, in the county since 2014.

Separately on Tuesday, an improvised explosive device that officials said was planted by al-Shabab to target a police car instead struck a Toyota Land Cruiser near the Somalia border. A senior police official, who spoke on condition of anonymity because he was not authorized to give media the information, said all four occupants of the vehicle were killed, including a child, in the attack near Liboi town.

Kenya has managed to stop the frequency of al-Shabab attacks in its capital, Nairobi, and major towns, but human rights groups say the government uses methods such as extrajudicial killings that can fuel revenge attacks.