Kenya's security agencies in the coastal county of Lamu have intensified a crackdown on suspected al-Shabab militants following an ambush that killed one officer and injuring two others on Thursday.

Lamu County Administration Police Coordinating Commander Charles Mbatu said the crackdown is concentrated around the area of the attack at Milihoi and areas toward and around the Boni forest where the militants are said to have fled shortly after the daytime attack.

"We lost an officer who had been injured in the attack. Two others were injured. Two vehicles are also torched. We are still very much on the ground pursuing the suspects," Mbatu said in Lamu.

The Boni forest has been used as the hideout by militants when they launch attacks in Lamu. There were reports that the militants have a well-equipped base deep inside the forest.

The scene of the latest attack, on the Lamu-Garsen road, is a secluded location where militants launched tens of attacks on security and civilian vehicles in the past.

Two vehicles, the police vehicle and a private saloon car that was heading to Lamu, were torched during the daring ambush.

The police vehicle had six officers on board. Three remain accounted for, said Mbatu.

The private vehicle had two occupants who managed to escape, though their whereabouts remain unknown, raising fears that they could have been killed by the militants after they fled into the bushes for cover or taken hostage by the militants.

The attack paralyzed transport on the road for hours.

Transport has since resumed amid heavy security presence on the road and surrounding bushes.