An Afghan official says the northern city of Kunduz has been captured by the Taliban after hours of clashes with security forces.
The fall of Kunduz on September 28 marks a major setback for government forces, who have struggled to fend off the Taliban since the withdrawal of most international troops last year.
The capture of Kunduz by the Taliban is the first time Afghan security forces have abandoned a provincial headquarters in the last 14 years.
Interior Ministry spokesman Sediq Sediqqi told the Associated Press news agency that "Kunduz city has collapsed into the hands of the Taliban."
"Security forces in Kunduz were prepared for an attack, but not one of this size, and not one that was coordinated in 10 different locations at the same time," said Sediqqi.
Sediqqi said military reinforcements have been sent to Kunduz, where government forces managed to fend off a major Taliban assault earlier this year.
"We are trying our best to clear the city as soon as possible," Sediqqi said.
The Taliban used social media to claim the "conquest" of Kunduz.
The capture of Kunduz by the Taliban is the first time Afghan security forces have abandoned a provincial headquarters in the last 14 years.
A statement attributed to the group's new leader, Mullah Akhtar Mansur, said: "The citizens of Kunduz should not worry about safeguarding their lives and properties. Carry out your ordinary livelihoods in absolute security. All traders, workers, staff of hospitals, municipality and governing bodies should continue their daily routines without any fear or intimidation."
But residents complained that Taliban fighters were looting shops and had burned down one radio station in the city.
During their reign from 1996-2001, the Taliban implemented Shari'a law in areas under their control, including banning girls from going to school and outlawing music.
The Taliban said earlier that it had seized the provincial government headquarters in Kunduz and was moving toward the main airport where some government officials had fled.
Hundreds of panicked residents were also streaming to the airport in an effort to flee.
Militants raised the white Taliban banner over the central city square and freed hundreds of fellow militants from the local jail.
Afghan special forces were being flown from Kabul and neighboring provinces into Kunduz in a bid to retake the city.
The deputy spokesman for President Ashraf Ghani had earlier described the situation in Kunduz as "fluid."
Zafar Hashemi said the president was "in constant contact with the security and defense leadership to provide them with guidance."
"Our first priority is the safety and security of residents," he said.
The medical charity Doctors Without Borders said it had treated more than 100 wounded people in Kunduz since the assault began, including 36 who were "in critical condition, with severe abdominal and head injuries."
Afghan security officials in Kunduz said both the Taliban and Afghan forces had sustained heavy casualties.
Meanwhile, the United Nations Assistance Mission in Afghanistan evacuated its Kunduz compound on September 28, soon after the assault began.
"They've been relocated within Afghanistan," said UN spokesman Dominic Medley, declining to say where or how many staff were evacuated.
The once-quiet north of Afghanistan has seen escalating violence in recent years.
Kunduz city was the center of fierce fighting in April as the Taliban sought to gain territory after NATO ended its combat mission in Afghanistan last December and pulled out the bulk of its troops.
Kunduz Province contains major roads that connect central and northern Afghanistan, including a road to the capital, Kabul.