KUNDUZ: United States (US) military planes hit Taliban positions on the outskirts of the fallen northern Afghan city of Kunduz on Tuesday, a Nato spokesman said, as Afghan national forces launched a counter-attack to try to retake the city.

The attack at about 9 am marked the first US air strike to defend the city.

"US forces conducted an air strike in Kunduz today to eliminate a threat to coalition and Afghan forces operating in the vicinity of Kunduz," said Colonel Brian Tribus, a spokesman for the Nato-led coalition. He did not elaborate on how many coalition forces troops were in the area.

Afghan army launches offensive to retake Kunduz city from Taliban

The Afghan army on Tuesday launched a counter-offensive to retake Kunduz from the Taliban, a day after insurgents overran the strategic northern city.

"Afghan army reinforcements began the operation to recapture Kunduz city at 8:00 am today," the defence ministry said in a statement. “The police headquarters and city prison have been retaken."

The stunning 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 spotlighted the insurgency's potential to expand beyond its rural strongholds.

Deputy Interior Minister Ayoub Salangi said security forces were ready to retake the city and vowed to investigate how the Taliban managed to seize a major urban centre for the first time in 14 years.

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

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

Kunduz was swarming with Taliban fighters racing stolen police vehicles, who officials said overran the governor's compound and the local police headquarters.

The local headquarters of the National Directorate of Security, the country's main intelligence agency, was set on fire and a 200-bed government bed was also captured.

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

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 militants largely on their own.

The fall of the city coincides with the first anniversary of President Ashraf Ghani's national unity government coming to power, as it struggles to rein in the ascendant insurgency.

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

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 late Monday, Mansour congratulated his cadres over the "major victory".

After years of costly involvement, most Nato troops pulled back from the frontlines by the end of 2014, although a residual force of around 13,000 remains for training and counter-terrorism operations.

Peace overtures by the government of President Ghani over the summer ended in failure, as civilian casualties soared to a record high in the first half of 2015 according to a United Nations (UN) report.

Key dates in the rise of the Afghan Taliban

Here is a timeline of key events in the rise of the fundamentalist movement:

• 1979-1989: The Soviet Union sends troops into Afghanistan to prop up a communist regime but faces fierce resistance from Afghan mujahideen fighters backed by the West. Moscow withdraws in February 1989 after a decade of fighting.

• 1992-1996: The fall of Mohammad Najibullah's government in 1992 unleashes a bloody power struggle that kills nearly 100,000 people in two years and sees fundamentalist Taliban movement begin to emerge in the south.

• 1996-2001: The Taliban, led by Mullah Mohammad Omar, take power in 1996 and install a regime based on a hardline interpretation of Islamic law. They become close to Al Qaeda and shelter its leader Osama bin Laden.

• September, 2001: Al Qaeda hijackers fly passenger planes into the World Trade Center and the Pentagon in the US, killing nearly 3,000 people.

• October, 2001: A US-led military campaign begins with air strikes against Afghanistan, followed by an invasion, to hunt down bin Laden and topple the Taliban.

• December 2001: The Taliban are forced from power and Nato-led forces are deployed to support the new interim government.

• October, 2004: Interim leader Hamid Karzai wins Afghanistan's first presidential election.

• February 2007: US president George W Bush vows to further boost his country's forces after an attack on a US base during a visit by vice president Dick Cheney.

• June, 2007: Dozens are killed in a string of suicide attacks, including one in a factory north of Kabul that claims 79 lives.

• November 2008: Democrat Barack Obama is elected US president, vowing to end the war in Iraq and focus on Afghanistan.

• November 2009: Karzai wins another term as president but is accused of massive fraud.

• December, 2009: Obama orders a "surge" of 30,000 troops but says withdrawals will begin in July 2011. Nato-led troops reach a peak of 150,000 in the summer of 2010.

• 2011: A string of suicide attacks claim hundreds of lives culminating in multiple blasts on the day of Ashura in December that kill at least 84 people.

• May, 2011: Osama bin Laden is killed by US special forces in the Pakistani garrison town of Abbottabad, prompting calls for the war in Afghanistan to end.

• June 2011: Obama announces the withdrawal of 33,000 US troops by the middle of 2012 and Western powers start handing authority to Afghan forces and officials.

• June 2013: Afghan forces take control of security from Nato forces as US-led combat troops prepare their final withdrawal.

• September, 2014: New president Ashraf Ghani takes power.

• December, 2014: Nato ends its combat mission in Afghanistan.

• April, 2015: The Taliban vow nationwide attacks as part of its annual "spring offensive", but face defections to the self-styled Islamic State.

• July, 2015: The first peace talks between Taliban representatives and the Afghan government are suspended indefinitely after news of the death of Mullah Omar.

• September, 2015: Taliban insurgents seize Kunduz.