HERAT, Afghanistan - Five Afghan border policemen were killed in a so-called insider attack in Kushk-i- Kuhna district of western Afghanistan's Herat province over, sources said on Monday.

"According to initial reports, a member of Afghan Border Police (ABP) named Bismillah was involved in shooting incident in a border outpost in the district, northern of provincial capital of Herat city midnight, killing five cops," a provincial ABP senior official Juma Gul Adil told Xinhua.

The attacker reportedly fled and joined the Taliban insurgent group in the district bordering Turkmenitan, sources said.

Over the past years, hundreds of the Afghan forces and foreign soldiers had been killed in the so-called insider attacks in the war-torn country. Taliban had in the past claimed responsibility for insider attacks. ?

This is the first such attack so far this year.

The Afghan soldiers and police casualties have risen recently as the United States and NATO troops in Afghanistan switched from combat to support role, namely training, advising and assisting Afghan forces.

Afghan security forces took the full operational lead from foreign troops in June last year.

The war-torn country is due to take over the responsibility for its own security from foreign troops by the end of 2014.

More than 57,000-strong NATO-led foreign troops, down from the peak of 130,000 in 2010, currently are being deployed in Afghanistan.