Afghanistan has mobilised military reinforcements for a counteroffensive to take back Kunduz, a day after Taliban fighters overran the strategic northern city in their biggest victory since being toppled from power in 2001.

Afghan security forces have retreated to the outlying airport, leaving the Taliban effectively in control of Kunduz after they stormed the city, capturing government buildings and freeing hundreds of prisoners.

Scores of unidentified bodies littered the streets after hours of heavy fighting on Monday, according to local residents, many of whom were making a hasty exit from Kunduz, some by road while others headed to the airport.

Ayoub Salangi, Afghan deputy interior minister, said security forces were ready to retake the city and pledged to investigate how the Taliban managed to seize a major urban centre for the first time in 14 years.

The fall of the provincial capital, which has sent panicked residents fleeing, has dealt a major blow to the country’s NATO-trained security forces and highlighted the insurgency’s potential to expand beyond its rural strongholds.

Ghani’s anniversary

The development also coincides with the first anniversary of President Ashraf Ghani’s national unity government coming to power, as it struggles to contain the insurgency.

It will, furthermore, boost the image of new Taliban leader Mullah Akhtar Mansoor within insurgent ranks as he seeks to drive attention away from internal rifts over his leadership.

“Yes, the enemy is in the city and they have taken over the prison and other buildings, but reinforcements are being deployed and the city will be taken back,” Sediq Sediqqi, interior ministry spokesman, told AFP news agency on Monday.

3. So who is the loser here again? The government that was duped so easily by word of these militia commanders..when everyone saw through it
— Mujib Mashal (@MujMash) September 29, 2015

Zabiullah Mujahid, Taliban spokesman, posted a triumphant picture on Twitter purportedly showing fighters raising the group’s trademark white flag at a roundabout in the city centre.

The Taliban also stormed the local jail, freeing hundreds of prisoners including some Taliban commanders, officials said.

The Taliban’s incursion into Kunduz barely nine months after the NATO combat mission concluded raises troubling questions over the capacity of Afghan forces as they battle the fighters largely on their own.

Kunduz province, which borders Tajikistan and is a major transport hub for the north of the country, could offer the Taliban a critical new base of operations beyond their traditional southern strongholds.

In a statement released on Monday, Mansoor congratulated his cadres over the “major victory”.

Before Monday’s incursion, the Taliban made two attempts this year to capture Kunduz city, which has encircled by the fighters for around a year now.

“As fighting rages in Kunduz, all sides must ensure that civilians and civilian objects are protected according to international humanitarian law,” Amnesty International, the human-rights organisation, said in a statement.

“Reports that the Taliban have already sent armed fighters into a public provincial hospital are extremely worrying.”

The Taliban has been largely absent from Afghan cities since being driven from power by the US and its allies, but has maintained rule over swathes of the countryside.

The Taliban has been waging an insurgency since a US-led invasion removed them from power in late 2001.

Kunduz was the last Taliban stronghold in northern Afghanistan then.

The fighters have stepped up attacks, starting with an offensive launched in late April against the internationally recognised government in Kabul. Al Jazeera