By Feisal Omar

MOGADISHU Dec 27 (Reuters) - The Somali Islamist group al Shabaab said it ambushed a Kenyan security vehicle in remote northeastern Kenya on Sunday, killing four members of the security forces.

The Kenyan Red Cross said in a post on Twitter that two police officers had been killed and two others injured, while a Kenyan police spokesman said he was unaware of the attack.

"Security has been beefed up in the region. Tension remains high," the Red Cross said.

Sheikh Abdiasis Abu Musab, al Shabaab's military spokesman, told Reuters the militants had ambushed the car on the main road in Mandera County, on the Somali border, killing four Kenyan soldiers, and seizing their weapons.

The statement made no mention of police.

Al Shabaab and officials often given conflicting details and death tolls.

Al Shabaab, which seeks to overthrow Somalia's Western-backed government and impose a strict version of Sharia law, has carried out regular assaults in neighbouring Kenya in retaliation for Kenya contributing troops to an African Union peacekeeping force in Somalia.

The attack in Mandera County came two days after al Shabaab, which has links to al Qaeda, targeted two Kenyan security vehicles in Lamu County, killing at least one police officer. (Additional reporting by Joseph Akwiri; Editing by Edith Honan and Andrew Bolton)