An air strike has killed at least 17 members of Afghanistan's anti-narcotics special forces who were on a mission in the province of Helmand, local government officials told Al Jazeera.

Omar Zwak, a spokesman for the governor of Helmand province, told Al Jazeera on Monday that the "foreign air strike" that killed the government troops took place on Sunday evening.  

Ayoub Omar Omari, district governor of Garamsir in Helmand, also confirmed the report to Al Jazeera, adding that the vehicles of the special forces were hit in an area named Registan, between the provinces of Kandahar and Helmand.

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The area is where the government's anti-drug police forces regularly set up ambushes to intercept drug smugglers.

Another Afghan official told the Associated Press news agency that the air strike was committed by NATO forces and came during an operation that was meant to arrest drug-smuggling suspects.

Al Jazeera has contacted NATO and the US-led coalition forces, but they have yet to comment on the reported strike.

NATO ended its combat mission in Afghanistan in December 2014, pulling out the bulk of its troops - although a 13,000-strong residual force remains for training and counterterrorism operations.

Stretched on multiple fronts as the Taliban's campaign expands, Afghan forces are facing their first fighting season without the full support of US-led NATO forces.

The Taliban are stepping up their summer offensive, launched in late April, amid a bitter leadership dispute following the announcement of the death of longtime leader Mullah Omar.

Mullah Akhtar Mansour, Omar's trusted deputy, was named as the new Taliban chief in late July.

Source: Al Jazeera and agencies