Afghanistan's security forces are coming under heavy fire as they battle to retake the city of Kunduz from the Taliban.
Tuesday's counter-offensive was taking place as the Taliban was said to be closing in on the city's airport after many of the security forces had fled.
Al Jazeera's Qais Azimy, reporting from Baghlan, just south of Kunduz, said Taliban fighters were close to the airport where machine gunfire could reportedly be heard.
"Afghan security forces and other government employees are inside. They fled to the airport, they thought it was the safest place," our correspondent said.
Earlier on Tuesday, Afghanistan's President Ashraf Ghani, in an address to the nation, said security forces had retaken some government buildings and that the Taliban had "sustained heavy casualties".
Afghanistan mobilised military reinforcements 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.
The US carried out two air strikes in support of the government.
In Washington, Pentagon spokesman Peter Cook "strongly" condemned the Taliban attack and confirmed that "limited coalition forces" were on the ground in the Kunduz area involved in "training, advising and assisting the Afghan security forces in accordance with our resolute support mission".
The first strike by a US plane, he said was carried out "in order to eliminate a threat to coalition and Afghan forces in the area".
The single bomb dropped was said to have destroyed a tank stolen by the Taliban.
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Many of the Afghan security forces 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.
The number of dead and wounded in the fighting was unclear as overwhelmed health workers struggled to treat the injured and verify how many had died.
"We fear that many more civilians may be harmed if fighting continues over the next few days," UN High Commissioner for Human Rights Zeid Ra'ad Al Hussein said, adding that the UN was "seeking to verify reports that at least 110 civilians were killed and injured".
Many residents were making a hasty exit from Kunduz, some by road while others headed to the airport.
Al Jazeera's Azimy said government troops who attempted to re-enter the city were foiled by intense gun battles.
Ayoub Salangi, the deputy interior minister, said security forces were ready to retake Kunduz and pledged to investigate how the Taliban managed to seize a major urban centre for the first time in 14 years.
However, the government forces faced intense resistance, with Taliban fighters blocking roads, carrying out ambushes and setting roadside explosives. Power lines were also cut to foil a government counterattack, sources told Al Jazeera.
The fall of Kunduz 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.
The fighters reportedly freed almost 600 prisoners, mostly former Taliban members, from jails in the city.
Zabiullah Mujahid, the 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.
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Before Monday's incursion, the Taliban made two attempts this year to capture Kunduz city, which has been encircled by the fighters for around a year.
The group has been largely absent from Afghan cities since being driven from power by the US and its allies, but has maintained rule over swaths of the countryside.
Taliban prisoners walk on a street after their comrades released them from the main jain in Kunduz city [AP]
Source: Al Jazeera and agencies