Kenyan police are pursuing suspected Somali Islamist militants who attacked a police post near the border late Saturday. As Derek Kilner reports from Nairobi, the border with lawless Somalia to the North has long been a concern for Kenya.

On Saturday night, gunmen attacked a police post at Dadajabulla in Kenya's Northeastern province, near the border with Somalia. Kenyan police say two officers were injured in the attack.

The gunmen freed three foreigners who had been detained earlier in the day by the police for being in the country illegally. Kenyan media have reported that the men are suspected of involvement with Islamist militants and that at least one of those detained is thought to be a British citizen.

Residents have said the attackers, who may have numbered as many as 50 according to local news reports, were members of the Shabaab, a radical Islamist insurgent group fighting Somalia's Transitional Federal Government, which is backed by Ethiopian troops.

Kenyan police spokesman Eric Kiraithe said the precise identity of the attackers is unknown but that they were members of a Somali militia. He said the police would go after the militants, but declined to say whether that would involve operations across the border in Somalia.

"One thing is for sure. They must pay for their sins,"

Kiraithe said. "They have committed a very serious crime against Kenyans. They can't do that in Kenya. We know they are lawless there but if you want to extend it to Kenya then we must say a very firm no. Kenyans must be secure."

The militants also stole firearms and a Land Cruiser from the police in the raid.

Security along the border with Somalia has long been a concern for Kenyan police. There are worries that a new wave of refugees caused by intensified fighting in Somalia in recent months could allow militants into the country.

In June 2007, two Kenyan police officers were abducted and killed along the border with Somalia.

Islamist militants have strengthened their presence in southern Somalia in recent weeks. Somalia's Radio Shabelle reported that militants had taken control of the town of Kudha, near the Kenyan border, on Friday.