The Taliban on Monday continued its advance further into Afghanistan amid U.S. withdrawal, advancing in areas where the U.S. military no longer carries out many airstrikes, officials say. 

In just 48 hours, the Taliban captured six provincial capitals in northern and western Afghanistan. 

With Bagram Air Base closed, the U.S. military is now forced to fly drones, B-52 bombers and AC-130 gunships from bases in Qatar and the United Arab Emirates. The eight-hour flights leave little time overhead in Afghanistan and require coordination for Afghan special forces on the ground, which exist in the south but not up north, where the Taliban have taken a number of cities.

Smoke rises from damaged shops after fighting between Taliban and Afghan security forces in Kunduz city, northern Afghanistan, Sunday, Aug. 8, 2021. 

Smoke rises from damaged shops after fighting between Taliban and Afghan security forces in Kunduz city, northern Afghanistan, Sunday, Aug. 8, 2021.  (AP)

Officials say the airstrikes are keeping the volatile southern provinces of Kandahar and Helmand from falling into Taliban hands for the time being. 

Despite Taliban gains, U.S. officials have signaled no plans to step up airstrikes in Afghanistan. 

"When we look back, it's going to come down to leadership and what leadership was demonstrated, or not," by Afghans, Pentagon spokesman John Kirby said at a Monday news conference. "It's their country to defend now. It's their struggle."

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Senior officials from the White House National Security Council, State Department and Defense Department were in close contact with U.S. embassy officials in Kabul on Sunday assessing the broader impact of the fall of Kunduz, the largest and most significant Taliban takeover, according to a senior administration official. 

The administration official, however, indicated that the Biden administration remains determined to stick to its plan to end the U.S. war in Afghanistan by the end of the month despite the Taliban's rapid strategic gains.

Kirby refused to say how many airstrikes U.S. aircraft have done in recent days. And he declined to say whether the Biden administration might continue the airstrikes past President Biden's Aug. 31 withdrawal date, given the Taliban advance.

In the meantime, "we will continue to support them ... where and when feasible, understanding that it's not always going to be feasible,'' Kirby said of Afghan government and military leaders.

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The Biden administration says it will continue to support the Afghanistan military financially and logistically, including with contractors helping maintain the government's air force, from outside Afghanistan, after the withdrawal.

The Associated Press contributed to this report.