The Taliban completed their sweep of the country's south on Friday as they took four more provincial capitals in a lightning offensive that is gradually encircling Kabul, just weeks before the US is set to officially end its two-decade war.

The latest significant blow was the loss of the capital of Helmand province, where American, British and allied NATO forces fought some of the bloodiest battles in the past 20 years. Hundreds of foreign troops were killed in the province, which is also a major opium hub.

The insurgents have taken half of the country's 34 provincial capitals in recent days, including its second- and third-largest cities, Herat and Kandahar. The Taliban now control more than two-thirds of the country just weeks before the US plans to withdraw its last troops.

While the capital of Kabul isn't directly under threat yet, the losses and advances elsewhere further tighten the grip of a resurgent Taliban. The latest US military intelligence assessment suggests Kabul could come under insurgent pressure within 30 days and that, if current trends hold, the Taliban could gain full control of the country within a few months.

In the south, the insurgents swept through the capitals of Zabul and Uruzgan provinces, in addition to Helmand's.

Attaullah Afghan, the head of the provincial council in Helmand, said that the Taliban captured Lashkar Gah following weeks of heavy fighting and raised their white flag over governmental buildings. He said that three national army bases outside of Lashkar Gah remain under control of the government.

Atta Jan Haqbayan, the provincial council chief in Zabul province, said the local capital of Qalat fell and that officials were in a nearby army camp preparing to leave.

Bismillah Jan Mohammad and Qudratullah Rahimi, lawmakers from Afghanistan's southern Uruzgan province, said local officials surrendered Tirin Kot to the Taliban. Mohammad said the governor was heading to the airport to depart for Kabul.

In the country's west, meanwhile, Fazil Haq Ehsan, head of the provincial council in Ghor province, said its capital, Feroz Koh, also fell to the insurgents.

With security rapidly deteriorating, the United States planned to send in 3,000 troops to help evacuate some personnel from the US Embassy in Kabul. Separately, Britain said about 600 troops would be deployed on a short-term basis to support British nationals leaving the country, and Canada is sending special forces to help evacuate its embassy.

Thousands of Afghans have fled their homes amid fears the Taliban would again impose a brutal, repressive government, all but eliminating women's rights and conducting public executions.

Peace talks in Qatar remain stalled, though diplomats are still meeting, as the US, European and Asian nations warned that any government established by force would be rejected.

“We demand an immediate end to attacks against cities, urge a political settlement, and warn that a government imposed by force will be a pariah state,” said Zalmay Khalilzad, the US envoy to the talks.

But the Taliban advance continued, as they pushed into the capital of Logar province, just 80 kilometers south of Kabul.

Hasibullah Stanikzai, the head of the Logar provincial council, said fighting was still underway inside Puli-e Alim, with government forces holding the police headquarters and other security facilities. He spoke by phone from his office, and gunfire could be heard in the background. The Taliban said they had captured the police headquarters and a nearby prison.

The onslaught represents a stunning collapse of Afghan forces after the United States spent nearly two decades and USD 830 billion trying to establish a functioning state. US forces toppled the Taliban in the wake of the Sept. 11 attacks, which al-Qaida planned and executed while being sheltered by the Taliban government. The Taliban fighters now advancing across the country ride on American-made Humvees and carry M-16s pilfered from Afghan forces.

Bill Roggio, a senior fellow at the Foundation for Defense of Democracies, said the Afghan army has rotted from within due to corruption and mismanagement, leaving troops in the field poorly equipped and with little motivation to fight. The Taliban, meanwhile, have spent a decade taking control of large swaths of the countryside.

That allowed them to rapidly seize key infrastructure and urban areas once President Joe Biden announced the timeline for the US withdrawal, saying he was determined to end America's longest war.

“Whatever forces are left or remaining that are in the Kabul area and the provinces around them, they're going to be used for the defence of Kabul,” Roggio said.

?“Unless something dramatically changes, and I don't see how that's possible, these provinces (that have fallen) will remain under Taliban control."

?A day earlier, in Herat, Taliban fighters rushed past the Great Mosque in the historic city — a structure that dates to 500 BC and was once a spoil of Alexander the Great — and seized government buildings. Afghan lawmaker Semin Barekzai acknowledged the city's fall, saying that some officials there had escaped.

Herat had been under militant attack for two weeks, with one wave blunted by the arrival of warlord Ismail Khan and his forces. But on Thursday afternoon, Taliban fighters broke through the city's defensive lines.

The insurgents circulated photos and a video showing Khan in their captivity as well as video footage that appeared to show two Afghan military Black Hawk helicopters — provided by the US — that were captured in Herat. Later on Friday, they released photos showing two alleged looters being paraded through the streets with black makeup on their faces.

In Kandahar, the birthplace of the Taliban, insurgents seized the governor's office and other buildings, witnesses said. The governor and other officials fled the onslaught, catching a flight to Kabul, the witnesses added. They refused to be named publicly as the defeat has yet to be acknowledged by the government, which has not commented on the latest advances.

The Taliban had earlier attacked a prison in Kandahar and freed inmates inside, officials said.

Earlier Thursday, the militants raised their white flags imprinted with an Islamic proclamation of faith over the city of Ghazni, which sits on a crucial north-south highway just 130 kilometers (80 miles) southwest of Kabul.

The UN agency for humanitarian affairs warned that civilians in southern Afghanistan faced cut-off highways and mobile phone outages. It described aid groups as being unable to determine how many people had fled as intense fighting and airstrikes continued there.

On Thursday, Nasima Niazi, a lawmaker from Helmand, criticized airstrikes targeting the area, saying civilians likely had been wounded and killed. US Central Command has acknowledged carrying out several airstrikes in recent days, without providing details or commenting on the concerns over civilian casualties.

Pakistan meanwhile opened its Chaman border crossing for people who had been stranded in recent weeks. Juma Khan, the Pakistan border town's deputy commissioner, said the crossing was reopened following talks with the Taliban.

Even as diplomats met in Doha, Qatar on Thursday, the success of the Taliban offensive called into question whether they would ever rejoin long-stalled peace talks with the government in Kabul. Instead, the group could come to power by force — or the country could splinter into factional fighting like it did after the Soviet withdrawal in 1989.