Two Afghan officials and the Taliban say the militants have seized the provincial capital of Ghazni.
The capture Thursday marks the 10th provincial capital seized by the insurgents in the last week.
Fighting was still ongoing on the outskirts of the city. However, officials say the Taliban were raising their flag and the city had calmed after hours of heavy fighting.
The Afghan central government in Kabul and the security forces did not immediately acknowledge the capture of Ghazni.
Ghazni is some 80 miles southwest of Kabul.
The Taliban conquests are challenging the Biden administration's often-stated hopes that a desire for international legitimacy will moderate the Taliban's worst behavior.
On Tuesday, U.S. Afghanistan envoy Zalmay Khalilzad met with Taliban officials in Qatar to warn that they face pariah status if they seize power by force.
In a dig at President Joe Biden, Senate Minority Leader Mitch McConnell earlier this week mocked that diplomatic approach.
In answering questions following remarks on Tuesday, Biden stressed that he believed that the Afghani army still had the resources to defend the country against the Taliban.
(Afghanis) have to fight for themselves, fight for their nation," Biden said. "They have to want to fight; they have help."
At a press briefing on Tuesday, White House press secretary Jen Psaki defended the Biden administration's plan for withdrawal, saying that it was based on the "safety and security" of Americans.
"After 20 years at war, it's time to bring our troops home," she said.
Some analysts and former diplomats say while the new Taliban do show interest in international legitimacy, they've shown no sign of changing their behavior.