Al Shabab militants have killed five civilians, some by beheading, in eastern Kenya, a witness and a police source said.

The attack occurred on Saturday around 1630 GMT (7:30pm local) in the villages of Juhudi and Salama in Lamu county, which borders Somalia, the police source said.

"Five people were killed. The victims had their throats slit and there are others who were beheaded," the police said on Sunday.

"We have enhanced security in that area after the attack," Lamu County Commissioner Louis Rono said.

One resident, Hassan Abdul, said that "women were locked in the houses and the men ordered out, where they were tied with ropes and butchered".

A secondary school student was among the five people killed, Abdul said, adding that "all those killed were slashed and some of them had been beheaded".

Another local resident, Ismail Hussein, said that the militants stole food supplies before leaving, firing their arms into the air.

Ongoing deadly attacks

Based in Kenya's eastern neighbour Somalia, Al Shabab has been waging a bloody insurgency against the government in Mogadishu for more than 15 years.

Kenya first sent troops into Somalia in 2011 to combat the Al Qaeda-affiliated militants and is now a major contributor of troops to an African Union military operation against the group.

But it has suffered a string of retaliatory assaults, including a bloody siege at the Westgate mall in Nairobi in 2013 that cost 67 lives and an attack on Garissa University in 2015 that killed 148 people.

In Somalia itself, Al Shabab has continued to wage deadly attacks despite a major offensive launched last August by pro-government forces, backed by the AU force known as ATMIS.