In the latest assault on Afghan forces, who have faced devastating losses in recent years, Taliban fighters smashed through government defence lines near the city of Bala Murghab, capturing several checkpoints.

Jamshid Shahabi, the Badghis provincial governor's spokesman, said "around 10" police and soldiers were killed in heavy fighting that started before dawn and continued throughout the day.

The Taliban "are shelling the main bazaar of the district with mortars -- government forces are fighting back," Shahabi said.

In a statement, the defence ministry said Afghan forces had made a "tactical retreat" from a number of checkpoints in the district to "avoid civilian casualties".

Abdul Aziz Beg, the head of the Badghis provincial council, described the situation as "critical".

"If reinforcements are not urgently deployed, a catastrophe could happen in Bala Murghab district," Beg said.

The Taliban said they had conducted a coordinated attack on a series of government checkpoints, killing 12 security forces.

The clash comes as Zalmay Khalilzad, the US envoy tasked with forging a peace deal with the Taliban, is concluding a week-long visit to Afghanistan, where he has spoken to national leaders and stakeholders across the country.

In January, President Ashraf Ghani said 45,000 security forces had been killed since he took office in September 2014.