Four police officers were ambushed and killed on Friday in a coastal region of Kenya bordering Somalia that is prone to incursions by Al-Shabaab militants, according to a government official. The attack took place in Lamu County, where the government deployed security forces and declared a dusk-to-dawn curfew after the murder of seven civilians in a series of raids earlier this week.

“We had an incident today morning and we have lost four police officers. Their vehicle was hit and caught fire,” said Lamu County Commissioner Irungu Macharia.

“The attackers were being pursued”, he added.

A senior police officer in Lamu, speaking on condition of anonymity, said the vehicle was on patrol when it was “hit directly” by a rocket-propelled grenade.

There has not yet been any claim of responsibility for the attack. But the Lamu region, which includes the popular tourist beach destination of Lamu Island, lies close to the Somali frontier and has suffered frequent attacks, often carried out with roadside bombs.

Al-Shabaab fighters have staged several numerous raids inside Kenya in retaliation for Nairobi sending troops into Somalia in 2011 as part of an African Union force to oust the jihadists. Earlier this week, police initially suspected Al-Shabaab fighters were to blame for the killing of seven civilians in Lamu.

One man was beheaded and others shot or burned to death in two separate attacks over Sunday and Monday. But police later said the violence was linked to a local land dispute.

Kenya’s interior ministry on Wednesday declared parts of Lamu county “disturbed areas” and said a multi-agency security team would conduct a sweep for weapons in the region.