Afghan leaders have condemned a deadly weekend air strike that claimed the lives of civilians, which came at a time when NATO is trying to win public support while it roots out Taliban fighters from a southern stronghold.

The air strike occurred Sunday when NATO planes fired at a convoy of three minibuses which were perceived to be a group of insurgents. Instead, the vehicles carried 42 civilians, including at least four women and one child who died in the attack in Uruzgan province.

The exact number of dead was not immediately clear, as the Afghanistan Council of Ministers said 27 people had died, revising initial reports that said 33 were killed in what it termed an "unjustifiable" attack. Those numbers contrasted with a death toll of 21 people that an Interior Ministry spokesperson told The Canadian Press, as well as a figure of 15 dead that Uruzgan Gov. Assadullah Hamdam provided.

CTV's South Asia Bureau Chief, Janis Mackey Frayer, said part of the problem stemmed from the fact that Uruzgan is a remote province in central Afghanistan that is harder to access than those further south, including Kandahar and Helmand provinces.

"The numbers are being revised down," Mackey Frayer told CTV News Channel from Kandahar on Monday morning.

Frayer said it expected that it will take time for authorities to reach the scene and confirm the final numbers.

The minibuses were travelling on a major road near the border of two Afghan provinces, Uruzgan and Day Kundi, said Afghan Interior Ministry spokesperson Zemeri Bashary.

NATO has launched an investigation into the incident, as has the Afghan government.

U.S. General Stanley McChrystal, the top NATO commander in the war-torn country, issued an apology for the unintended deaths that resulted from the air strike.

"We are extremely saddened by the tragic loss of innocent lives," Gen. McChrystal said in the statement.

"I have made it clear to our forces that we are here to protect the Afghan people and inadvertently killing or injuring civilians undermines their trust and confidence in our mission. We will redouble our effort to regain that trust."

Last summer, McChrystal said that NATO forces would do everything in their power to minimize the risk to Afghan civilians.

"This would represent, perhaps, the gravest error, the gravest violation of that McChrystal policy in the last six months," Frayer said, referring to the weekend deaths in Uruzgan province.

Following the news of the deadly incident on Sunday, Afghan President Hamid Karzai said NATO must do more to protect Afghan lives when conducting military operations.

"We need to reach the point where there are no civilian casualties," Karzai said. "Our effort and our criticism will continue until we reach that goal."

The Afghanistan Council of Ministers urged NATO to "closely coordinate and exercise maximum care before conduction any military operation."

Moshtarak challenges

Sunday's deaths marked the third time that noncombatants had been killed by an air strike since the start of a major NATO offensive in Helmand province -- known as Operation Moshtarak -- targeting the Taliban fighters stationed in the city of Marjah.

The offensive, which launched earlier this month, also seeks to win the support of the Afghan people and to eventually restore government rule in Marjah, which is considered a Taliban stronghold.

A pair of NATO rockets killed 12 people at a home in Marjah last week, while an air strike in northern Kunduz province killed seven policemen.

Despite the ongoing fighting between NATO forces and Taliban insurgents, district leader Abdul Zahir Aryan travelled to Marjah to begin planning for to return of government administration in the city.

He met with about 50 community elders, said Capt. Abe Sipe, a spokesperson for the U.S. Marines.

"The Marines have told us that the situation is better. It's OK. It's good," Aryan said. "I'm not scared because it is my home. I have come to serve the people."

Last year. Afghanistan saw more than 2,400 civilians killed -- the highest number of civilian deaths since the start of the eight-year war -- according to a recent UN report.

But Afghan deaths attributed to NATO plunged nearly 30 per cent, the report said, because of new rules that limit the use air power and heavy weapons when civilians are present.

Suicide bombing

Elsewhere in Afghanistan, a suicide bomber killed 15 people Monday outside of Jalalabad, the capital of Nangarhar province.

The attack happened in the Khogyani district when a group of tribal elders were meeting with several hundred Afghan refugees who had come back from Pakistan, said Police Gen. Mohammad Ayub Salangi. Government workers were also at the scene.

Among the dead was Mohammad Zaman Ghamsharik, an ex-mujahedeen fighter who once cornered Osama bin Laden in the mountains of Nangarhar province in 2001, but was unable to keep the wanted al Qaeda leader from slipping away.

With files from The Associated Press and The Canadian Press