Afghan forces who reported being under Taliban fire requested the U.S. airstrike that killed 22 people at a medical clinic in northern Afghanistan over the weekend, the top commander of American and coalition forces in Afghanistan said Monday, correcting an initial U.S. statement that the strike had been launched because U.S. forces were threatened.

The strike wasn't sought by U.S. forces, Gen. John F. Campbell said at a hastily arranged Pentagon news conference.

"We have now learned that on Oct. 3, Afghan forces advised that they were taking fire from enemy positions and asked for air support from U.S. forces," Campbell said. "An airstrike was then called to eliminate the Taliban threat and several civilians were accidentally struck. This is different from the initial reports, which indicated that U.S. forces were threatened and that the airstrike was called on their behalf."

The clinic was operated by the medical charity Doctors Without Borders. The attack killed at least 22 people and wounded dozens more, setting the hospital on fire.

In response to Campbell's remarks, the organization's general director, Christopher Stokes, said the U.S. had admitted that it attacked the facility.

If errors were committed we will acknowledge them. - Gen. John F. Campbell

"The U.S. military remains responsible for the targets it hits, even though it is part of a coalition," Stokes said. "There can be no justification for this horrible attack. With such constant discrepancies in the U.S. and Afghan accounts of what happened, the need for a full transparent independent investigation is ever more critical."

On Saturday, Afghan officials said Taliban fighters were in the hospital at the time of the airstrike, but that is in dispute.

On Sunday, NATO, under whose umbrella the U.S.-led coalition operates in Afghanistan, issued a statement saying U.S. forces had conducted an airstrike against "insurgents who were directly firing upon U.S. service members" who were advising Afghan forces in Kunduz. The statement also said NATO was undertaking a preliminary assessment of the incident by a multi-national "casualty assessment team," and that it would produce initial results "in a matter of days."

The U.S. military is doing its own standard investigation under the Uniform Code of Military Justice.

Unclear whether clinic was targeted

Campbell's revised account does not clarify whether the clinic was targeted in error or whether U.S. military personnel followed procedure. They are required to verify that the target of the requested airstrike is valid before firing. Asked about those procedures, Campbell said he would not discuss the rules of engagement under which U.S. forces operate.

"If errors were committed we will acknowledge them," Campbell said. "We'll hold those responsible accountable and we'll take steps to ensure mistakes are not repeated."

Asked whether he could confirm in general terms whether hospitals and other civilian facilities like mosques and schools are off limits to U.S. airstrikes, Campbell replied, "Very broadly, we do not strike those kind of targets, absolutely."

The burnt shell of a Doctors Without Borders hospital in the northern Afghan city of Kunduz after an airstrike hit on Saturday. The U.S. was set to comment Monday on the bombing, which some say was collateral damage from a U.S. attack on the Taliban. (Médecins Sans Frontières/Associated Press) He declined to say who authorized the strike. He said it was carried out by an AC-130 gunship, which is an Air Force special operations aircraft sometimes used against close-range ground targets. The aircraft is armed with side-firing weapons including 40mm and 105mm cannons and a 25mm Gatling gun.

Campbell declined to provide more details, saying military investigations by the U.S. as well as Afghanistan are ongoing. He said he learned from the U.S. military's lead investigator that it was the Afghans, not the Americans, who requested the airstrike.

Clashes still underway

Residents of Kunduz began venturing out of their homes as calm returned to the streets on Monday, officials said, in the first signs of normalcy following the deadly Taliban blitz last week that captured and held Kunduz for three days.

But clashes were still underway between government forces and the Taliban along Kunduz's northern, southern and eastern outskirts on Monday, according to Khosh Mohammad, a member of the Kunduz provincial council.

Meanwhile, the medical charity Doctors Without Borders (also known by its French name Médecins Sans Frontières, or MSF) continued to press U.S. and Afghan officials for an independent investigation into the bombing early Saturday of its hospital.

Christopher Stokes, the general director of MSF, said Monday he was "disgusted by the recent statements coming from some Afghanistan government authorities justifying the attack."

"These statements imply that Afghan and U.S. forces working together decided to raze to the ground a fully functioning hospital," Stokes was quoted as saying in the statement.

Obama awaits full accounting

President Barack Obama said he expected a full accounting of the circumstances surrounding the bombing, and that he would wait for those results before making a judgment.

In the centre of Kunduz, shops opened and people were seen walking the streets Monday, said Sarwar Hussaini, spokesman for the provincial police chief. Government troops have largely cleared the militants from the city after launching a counter-offensive last Thursday, he added.

Kunduz is an important city on the Tajikistan border, a hub for smuggling routes for drugs and guns to and from Central Asian countries, and alcohol into Afghanistan, officials have said.