The government flew hundreds of commandos into Qala-i-Naw, in northwestern Badghis province, the first regional capital to face an all-out assault by the Taliban since the United States stepped up its troop withdrawal.

With the US pullout "90 percent complete", according to the Pentagon, the insurgents have launched a blistering campaign to capture new territory, and fears are mounting that Afghan forces will collapse without vital American air support.

In London, Prime Minister Boris Johnson said most British troops had now left Afghanistan as part of a NATO withdrawal in parallel to the US pullout.

"I will not disclose the timetable of our departure, but I can tell the House that most of our personnel have already left," he said in a statement to MPs Thursday.

US President Joe Biden was due to speak on the US pullout later in the day after meeting his national security team.

The withdrawals have drastically emboldened the Taliban, and video obtained by AFP showed thick smoke billowing over Qala-i-Naw Thursday, soundtracked by gunfire, as fighting raged.

Badghis health official Abdul Latif Rostaee said at least 10 civilians had been taken to hospital since the fighting erupted.

"The Taliban have resumed their attacks from several directions with light and heavy weapons," Badghis Governor Hessamuddin Shams told AFP on Thursday.

"Our security forces are bravely fighting them and the enemy is being pushed back. They are fleeing. We will give a hard blow to the enemy."

On Wednesday, the Taliban briefly seized the police headquarters and the local office of the country's spy agency, but were later pushed back.

Qala-i-Naw resident Aziz Tawakoli said Taliban fighters were still roaming the city, however.

"You can see them going up and down the streets on their motorcycles," he said.

Tawakoli said many of the city's 75,000 people had fled their homes -- either to nearby districts or to neighbouring Herat province.

"The shops are closed and there is hardly anyone on the streets," he said, adding that helicopters and planes had bombed Taliban targets through the night.

Badghis provincial council member Zia Gul Habibi said the Taliban suffered casualties, but also surrounded the city.

"All districts are under their control... People are really in fear," she said.

"All shops and government institutions are closed. There are still reports of sporadic fighting."