KANDAHAR: Four Afghan policemen were shot dead and three wounded after being poisoned by a colleague in southern Afghanistan on Wednesday, officials said.

The attack happened in the Spin Boldak district of Kandahar province and is the latest in a series of insider attacks by Afghan security forces on their local and foreign colleagues.

“There were eight border police in Shero area check post, one of them poisoned the others' food and then shot them,” provincial spokesman Jawid Faysal told AFP.

Four had died and three taken to hospital for treatment for gunshot wounds while the attacker had fled, he said.

Ghurzang Afridi, a spokesman for border police in southern Afghanistan said a probe into the attack was under way.

“The police are still investigating whether the attacker had any links with Taliban,” he said.

Afghan police are an important force in supporting US-led Nato forces in the fight against Taliban militants, but they are poorly equipped and often susceptible to Taliban infiltration.

Afghanistan has witnessed a surge in insider attacks this year, with more than 50 foreigners and dozens of local forces killed by their colleagues.

The unprecedented number of insider killings comes at a critical moment in the 11-year war, as US-led Nato forces plan to hand security responsibility to the Afghans ahead of a withdrawal of combat forces by the end of 2014.