KABUL: The Taliban captured the northern Afghan city of Kunduz in a massive assault Monday involving hundreds of fighters, and now control a major urban area for the first time since the 2001 U.S.-led invasion.

“Kunduz city has collapsed into the hands of the Taliban,” Interior Ministry spokesman Sediq Sediqqi told the Associated Press.

The fall of Kunduz marks a major setback for government forces, who have struggled to combat the Taliban since the U.S. and Nato shifted to a supporting role at the end of last year.

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.

In a multi-pronged assault that took military and intelligence agencies by surprise, the insurgents sent hundreds of fighters into Kunduz, a once-wealthy city at a key Central Asian crossroads, where they seized government buildings and freed hundreds of prisoners.

Residents said the militants reached the main square 12 hours after launching their attack. They said photographs of President Ashraf Ghani and other leaders were torn down and the white flag of the Taliban was raised. They said residents were streaming to the airport in an effort to flee.

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.”

The Taliban used social media to claim the “conquest” of Kunduz and reassure residents that the jobs of teachers, doctors and other civil employees, and their personal property, were safe. The Taliban have a history of brutality, and are known to ban women's education as well as music, movies and other trappings of modern life in areas they control.

Gen. Murad Ali Murad, the Deputy Chief of Army Staff, said the Monday attack involved a large number of Taliban drawn from across the north of the country and included foreign fighters. “Strategic areas, including the airport, are controlled by Afghan security forces,” he said.

“Reinforcements have already arrived and attacks on the insurgent positions will be launched soon,” he said without elaborating.

Sediqqi said the target of the Taliban assault was the city's main prison and police headquarters. “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,” he said.

Analyst Faheem Dashty said Afghan security and intelligence agencies had been “caught by surprise” in what appeared to be a “big failure” of security and intelligence. “They were expecting a big attack but couldn't defend the city.”

The Taliban launched their spring offensive earlier this year with a major assault on Kunduz that also took government forces unawares and was repelled with the aid of reinforcements after days of heavy fighting.

Since then the Taliban are believed to have regrouped and allied with other insurgents, including the Islamic Movement of Uzbekistan and militants driven into Afghanistan from neighboring Pakistan by a military assault on insurgent hideouts near the porous border.

A senior U.S. defense official, speaking on condition of anonymity in order to discuss an ongoing military operation, said the U.S. military was aware the Taliban had taken control of a hospital and a number of government buildings in the city, and that both sides - the Taliban and government forces - had sustained a significant number of casualties.

Early indications were that the Afghan forces were in position to throw back the attackers and regain control of the city, although the outcome was still in doubt, the official said earlier on Monday, before the government announced the fall of the city.

The Kunduz assault highlighted the resiliency of the Taliban following the revelation earlier this year that their reclusive longtime leader Mullah Mohammad Omar died two years ago. A bitter internal dispute over the appointment of his successor, Mullah Akhtar Mansoor, has yet to be fully resolved, but seems to have had little impact on the battlefield.