The Taliban seized the strategic Afghan city of Ghazni on Thursday, just 150 kilometers from Kabul, their most important gain in a lightning offensive that has seen them overrun 10 provincial capitals in a week.

The interior ministry confirmed the fall of the city, which lies along the major Kabul-Kandahar highway and serves as a gateway between the capital and militant strongholds in the south.

"The enemy took control," spokesman Mirwais Stanikzai said in a message to media, adding fighting and resistance was still going on.

The government has now effectively lost most of northern and western Afghanistan and is left holding a scattered archipelago of contested cities also dangerously at risk of falling to the Taliban.

The conflict has escalated dramatically since May, when U.S.-led forces began the final stage of a troop withdrawal due to end later this month following a 20-year occupation.

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The loss of Ghazni will likely pile more pressure on the country's already overstretched air force, needed to bolster Afghanistan's dispersed security forces who have increasingly been cut off from reinforcements by road.

Pro-Taliban social media accounts also boasted of the vast spoils of war their fighters had recovered in recent days, posting photos of armored vehicles, heavy weapons, and even a drone seized by the insurgents at abandoned Afghan military bases.

Inching closer

In less than a week the insurgents have taken 10 provincial capitals and encircled the biggest city in the north, the traditional anti-Taliban bastion of Mazar-i-Sharif. Fighting was also raging in Kandahar and Lashkar Gar – pro-Taliban heartlands in the south – as well as Herat in the west.

An official in Lashkar Gar said Taliban fighters were inching closer to government positions after a massive car bomb badly damaged the city's police headquarters Wednesday evening.

The blast forced local police to retreat to the governor's office, while around 40 of their colleagues and one senior commander surrendered to the Taliban.

And in Kandahar, the Taliban said they had overrun the heavily fortified jail in Kandahar, saying "hundreds of prisoners were released and taken to safety." The Taliban frequently target prisons to release incarcerated fighters and replenish their ranks. The loss of the prison is a further ominous sign for the country's second city, which has been besieged for weeks by the Taliban. 

Kandahar was once the stronghold of the Taliban – whose forces coalesced in the eponymously named province in the early 1990s – and its capture would serve as both a tactical and psychological victory for the militants.

'Deteriorating security situation'

Hundreds of thousands have been displaced by the fighting that has enveloped the country. In recent days, Kabul has been swamped by the displaced, who have begun camping out in parks and other public spaces, sparking a fresh humanitarian crisis in the already overtaxed capital.

In Washington, defense officials appeared to be grappling with the spiraling situation but insisted that Afghan security forces were still holding their ground.

"What we're seeing, a deteriorating security situation, we've been nothing but candid about that," Pentagon spokesman John Kirby told reporters Wednesday. 

"But there are places and there are times, including today, where Afghan forces in the field are putting up a fight."