An Afghan official says the Taliban attacked a police checkpoint in the southern Helmand province, killing five Afghan police.

Gen. Abdul Ghafar Safi, the provincial police chief, says six other policemen were wounded in the attack late Friday in Nawa district, where clashes were still underway early Saturday.

Taliban spokesman Qari Yusouf Ahmadi claimed responsibility for the attack.

The Taliban have stepped up their attacks since the U.S. and NATO formally concluded their combat mission at the end of 2014. In an "open letter" to U.S. President Donald Trump last week, the insurgent group reiterated its calls for the withdrawal of all remaining U.S. troops.

The United States has about 8,400 troops in Afghanistan, who support local forces and carry out counterterrorism operations.