ISLAMABAD - Officials in Afghanistan say four operatives of the national intelligence agency have gunned down their 16 colleagues before fleeing to join the Taliban insurgency in the southern Helmand province.

The rare overnight “insider” attack took place at a facility linked to the National Directorate of Security or NDS in the Gerishk district, security sources told VOA Sunday.

Omar Zawak, the provincial government spokesman, confirmed the incident saying the Taliban also assaulted the NDS Center while the insider attack was under way, sparking fierce clashes with Afghan security guards.

Zawak said both sides suffered heavy casualties but would not give further details.

Map showing Helmand province, Afghanistan Map showing Helmand province, Afghanistan Map showing Helmand province, Afghanistan

The Taliban claimed responsibility for the attack, saying it was carried out by three “infiltrators” who seized all weapons and equipment at the facility.

The slain Afghan personnel belonged to the “Songaryan” unit working for NDS in Helmand. The unit is named after a popular a Turkish television soap opera and has been playing a key role in gathering intelligence for NDS on the Taliban in volatile districts of Helmand.

Taliban sympathizers or infiltrators in Afghan army and police forces routinely carry out insider attacks, but such incidents are extremely rare at NDS-related installations in Afghanistan.

The insurgency controls or contests most of the 14 districts in Helmand, the largest Afghan province and one of the world’s major poppy producing regions.

The illegal narcotics trade funds 65 percent of insurgent activities, and the U.S. military has recently unleashed a new air campaign to destroy drug labs in a bid to disrupt Taliban financial resources in Helmand, which borders Pakistan.