The latest bloodshed underscores the insecurity across the Kunduz region, as NATO-backed Afghan forces continue to sustain losses in their struggle to beat back Taliban insurgents.

"Afghan forces and coalition troops conducted a joint operation against the Taliban," Kunduz's provincial spokesman Mahmood Danish said. "In the bombardment, 30 Afghan civilians were martyred and 25 others were wounded."

NATO conceded that it was behind the airstrikes, which it said were conducted "to defend friendly forces under fire." Two US soldiers were killed and a further four injured in an overnight raid. It remains unclear whether the deaths were linked to the subsequent airstrikes.

Both NATO and Afghan officials said they were also investigating the attack and its civilian causalities.

Commander of US Forces-Afghanistan General John Nicholson said in a statement: "Today's loss is heartbreaking and we offer our deepest condolences to the families and friends of our service members who lost their lives today."

A Kunduz hospital director said that his facility was treating 30 people, including children as young as three years old, wounded in the fighting.

Emotionally-charged protests ensued outside the governor's office in Kunduz in the aftermath of airstrikes, led by relatives of the airstrike victims carrying their bodies.

Relatives carry the bodies of the airstrike victims carry outside the Kunduz governor's office.

"I am heartbroken. I have lost seven members of my family. I want to know why these innocent children were killed?" said Taza Gul, a 55-year-old laborer. "Were they Taliban? No, they were innocent children."

Kunduz fighting intensifies

While it was not immediately clear whether the airstrikes were linked to the deaths of two US soldiers, the killings highlight the province's growing insecurity.

US Secretary of Defense Ash Carter that he was "deeply saddened" to hear of the US casualities. In a statement, Carter said: "Our service members were doing their part to help the Afghans secure their own country while protecting our homeland from those who would do us harm."

In October, Taliban forces overran the city of Kunduz, the province's state capital of the same name, for the second time in a year. Although the insurgents were pushed out on the same day, it served as a demonstration of strength and highlighted the troubles facing local Afghan forces since NATO operations in Afghanistan formally ended in 2014.

Last year, the Taliban held part of the city of Kunduz for a number of weeks. Afghan forces liberated the city with the help of US special unit forces and airstrikes. However, those strikes saw 42 people die in a hospital run by the medical charity Doctors Without Borders. Sixteen US military personnel, including a two-star general, were disciplined for what were described as "mistakes" leading to the airstrike. Doctors Without Borders has called the attack a war crime, demanding an independent investigation.

Since NATO's partial withdrawal from Afghanistan, leaving only residual forces offering training and support, local military forces have sustained heavy causalities as the Taliban continues to launch assaults on key regions, including Kunduz, Lashkar and Tarinkot. The worsening conflict has prompted US forces to step up aerial combat support, fueling speculation that it may be drawn back into the conflict.

dm/msh (AFP, Reuters, AP)