The Taliban captured two major Afghan cities, the country's second and third largest after Kabul, and a strategic provincial capital on Thursday, further squeezing the government just weeks before the end of the American military mission in Afghanistan.

The seizure of Kandahar and Herat marks the biggest prizes yet for the Taliban, who have taken 12 of Afghanistan's 34 provincial capitals as part of a weeklong blitz.

The capture of the city of Ghazni, meanwhile, cuts off a crucial highway linking the Afghan capital, Kabul, with the country's southern provinces, all part of an insurgent push some 20 years after U.S. and NATO troops invaded and ousted the Taliban government.

While Kabul itself isn't directly under threat yet, the losses and battles elsewhere further tighten the grip of a resurgent Taliban, who are estimated to now hold over two-thirds of the country and continue to press their offensive.

With security rapidly deteriorating, the United States planned to send in 3,000 troops to help evacuate some personnel from the U.S. Embassy in Kabul. Separately, Britain said about 600 troops would be deployed on a short-term basis to support British nationals leaving the country.

As the United Nations warned that a Taliban offensive reaching the capital would have a "catastrophic impact on civilians," the U.S., as well as Germany, urged their citizens to leave Afghanistan immediately.

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

Peace talks in Doha, Qatar, remain stalled, though diplomats met throughout the day. International envoys to Afghan negotiations called for an accelerated peace process as a "matter of great urgency," and for an immediate halt to attacks on cities.

Negotiators from the Afghan government are said to have offered the Taliban a power-sharing deal in return for an end to the violence in the country, Agence France-Presse (AFP) reported Thursday, citing a government negotiating source.

The latest U.S. 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. The Afghan government may eventually be forced to pull back to defend the capital and just a few other cities in the coming days if the Taliban keep up their momentum.

The onslaught represents a stunning collapse of Afghan forces and renews questions about where the over $830 billion spent by the U.S. Defense Department on fighting, training those troops and reconstruction efforts went – especially as Taliban fighters ride on American-made Humvees and pickup trucks with M-16s slung across their shoulders.

The speed of the Taliban offensive has sparked recriminations among many Afghans over President Joe Biden's decision to withdraw U.S. troops and leave the government to fight alone.

Biden said on Tuesday he does not regret his decision, noting that Washington has spent more than $1 trillion over 20 years in America's longest war and lost thousands of troops. He added the U.S. continues to provide significant air support, food, equipment and salaries to Afghan forces.

Afghan security forces and the government have not responded to repeated questions from journalists over the days of fighting, instead issuing video communiques that downplay the Taliban advance.

In Herat, Taliban fighters rushed past the Great Mosque in the historic city – which dates to 500 B.C. and was once a spoil of Alexander the Great – and seized government buildings. Witnesses described hearing sporadic gunfire at one government building while the rest of the city fell silent under the insurgents’ control.

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 and later said they were in control.

Afghan lawmaker Semin Barekzai also acknowledged the city's fall, saying that some officials there had escaped. Witnesses described seeing Taliban fighters once detained at Herat's prison now freely moving on the streets.

It wasn't immediately clear what happened to Khan, who earlier had been described as under attack with his forces at a government building.

In Kandahar, the Taliban 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 declined to be named publicly as the defeat has yet to be acknowledged by the government.

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, just 130 kilometers (80 miles) southwest of Kabul.

Ghazni provincial council member Amanullah Kamrani alleged that the provincial governor and police chief made a deal with the Taliban to flee after surrendering. Taliban video and photos purported to show the governor’s convoy freely passing by insurgents as part of the deal.

Afghan Interior Ministry spokesperson Mirwais Stanekzai later said the governor and his deputies had been arrested over that alleged deal. The officials could not be immediately reached for comment.

Stanekzai also acknowledged in a video message that parts of Ghazni had fallen, though he insisted government security forces "do exist" in the city.

The loss of Ghazni – which sits along the Kabul-Kandahar Highway – could complicate resupply and movement for government forces, as well as squeeze the capital from the south.

Already, the Taliban’s weeklong campaign has seen the militants seize nine other provincial capitals around the country. Many are in the country’s northeast corner, pressuring Kabul from that direction as well.

In southern Afghanistan, the Taliban’s heartland, heavy fighting continued in Lashkar Gah, where surrounded government forces hoped to hold onto the capital of Helmand province.

Nasima Niazi, a lawmaker from Helmand, criticized ongoing airstrikes targeting the area, saying civilians likely had been wounded and killed.

"The Taliban used civilian houses to protect themselves, and the government, without paying any attention to civilians, carried out airstrikes," she said.

With the Afghan air power limited and in disarray, aviation tracking data suggested U.S. Air Force B-52 bombers, F-15 fighter jets, drones and other aircraft were involved in the fighting across the country, according to Australia-based security firm The Cavell Group.

U.S. Air Force Maj. Nicole Ferrara, a Central Command spokesperson, acknowledged that American forces "have conducted several airstrikes in defense of our Afghan partners in recent days." However, she declined to offer any details on the attacks or to discuss the Afghan complaints of civilian casualties.

Late Thursday night, an Afghan official, speaking on condition of anonymity to discuss developments, said the Taliban have also taken much of western Badghis province – but not the provincial army corps and the intelligence department. A Taliban tweet claimed the insurgents captured the seat of the provincial governor, the police headquarters and all other government offices.

Even as diplomats met in Qatar, the success of the Taliban offensive called into question whether they would ever rejoin long-stalled peace talks aimed at moving Afghanistan toward an administration that includes members of the current Afghan government and the Taliban. 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.