The Taliban’s seemingly unstoppable advance across Afghanistan continued on Friday, as insurgents took control of four more provincial capitals after their seizure on Thursday of Kandahar and Herat, the country’s second and third biggest cities.

With Afghan forces in disarray, and amid reports that the country’s vice-president has fled, the Taliban are heading inexorably towards Kabul. They now control more than two-thirds of the country, just as the US plan to pull out its last remaining troops.

The latest US military intelligence assessment suggests Kabul could come under insurgent pressure within 30 days. If current trends continue the Taliban are likely gain full control of the country in a matter of months, it says.

The situation on the ground is changing at a dizzying pace. After a remorseless offensive in the north in which Herat fell, the Taliban have effortlessly consolidated ground in the south, the group’s traditional ethnic Pashtun base.

The group says it has seized Kandahar and is running the city. Attaullah Afghan, the head of the provincial council in Helmand, said the insurgents had also captured the provincial capital of Lashkar Gah after weeks of heavy fighting. They raised their white flag over governmentbuildings.

Atta Jan Haqbayan, the provincial chief in Zabul province, said the local capital of Qalat had also fallen. Tirin Kot in southern Uruzgan and Firuz Koh in central Ghor province surrendered too, a pattern of abandonment seen widely since the Taliban began their lightning advance eight days ago.

By Friday afternoon they had pushed into the capital of Logar province, just 50 miles south of Kabul. Hasibullah Stanikzai, the head of the Logar provincial council, said fighting was under way inside Puli-e Alim, and that government forces were holding the police headquarters and other security facilities.

Gunfire could be heard in the background as he spoke by phone from his office, the Associated Press reported. The Taliban said they had captured the police headquarters and a nearby prison.

Two decades after the US and UK turfed the Taliban out of Afghanistan in the wake of the 9/11 attacks, the group is on the brink of flipping the country back to hardline Islamist rule. The US and UK are scrambling to get most of their nationals out of Kabul.

The Biden administration said it was sending in 3,000 troops to help evacuate personnel from the US embassy. The UK said about 600 troops would be deployed on a short-term basis to support British nationals leaving. Canada is sending special forces to help clear out its embassy.

Even senior government figures appear to be leaving. Reports said Afghanistan’s first vice-president, Amrullah Saleh, had fled to neighbouring Tajikistan. In Herat, the veteran anti-Taliban warlord Ismail Khan gave himself up to insurgents, who said he had joined them.

Taliban fighters broke through Herat’s defences on Thursday afternoon, seizing administrative buildings and the police station. The city, on the border with Iran and with a great mosque dating back to 500BC, had been under bombardment for two weeks.

The insurgents circulated photos and a video showing Khan in their captivity and footage that appeared to show two Afghan Black Hawk helicopters provided by the US that were captured in Herat. Taliban fighters have been advancing in captured American humvees and armed with pilfered weapons.

“The city looks like a front line, a ghost town,” the provincial council member Ghulam Habib Hashimi said by telephone from Herat, a city of about 600,000 people. “Families have either left or are hiding in their homes,” he said.

Of Afghanistan’s major cities, the government still holds Kabul, Mazar-i-Sharif in the north, and Jalalabad near the Pakistani border in the east. The territory notionally under its control appears to be shrinking by the hour.

The UN said on Friday that a Taliban offensive on the capital would have a “catastrophic impact on civilians”. There appears little hope for negotiations which have been taking place in Doha, with the Taliban apparently set on a crushing military victory.

The speed of the offensive, as US-led foreign forces prepare to complete their withdrawal by the end of this month, has sparked recriminations over Joe Biden’s decision to withdraw .

The US president said this week that he did not regret his decision, noting that Washington has spent more than $1tn on America’s longest war and lost thousands of troops.