The top NATO commander in Afghanistan confirmed Saturday that civilians were wounded in an air strike on hijacked fuel tankers that killed up to 70 people.

U.S. Gen. Stanley McChrystal visited the area in Kunduz province where the strike occurred, as well as a hospital that took in many of the wounded. He stopped to speak to a 10-year-old boy who sustained severe burns to his arms and legs.

"From what I have seen today and going to the hospital, it's clear to me that there were some civilians that were harmed at the site," McChrystal told reporters.

However, while local officials declared that a number of civilians were killed in the strike, McChrystal did not say the same.

Early Friday, a U.S. F-15E Strike Eagle jet unloaded two 225-kilogram bombs on two fuel tankers that had been hijacked by the Taliban in Kunduz, just outside of the area's main town.

A fireball engulfed both militants and villagers, who had apparently crowded around the tankers to siphon off fuel.

During his visit to Kunduz, McChrystal had to wade through knee-high water to inspect the tankers.

McChrystal told reporters before visiting Kunduz Saturday that he wants to get to the bottom of what happened "so that we can prevent it from happening again -- or minimize the chances that it happens again -- and correct anything that we might be able to correct about it, like helping the injured."

There are many details that are still unclear about the incident, including why the air strike happened despite orders from McChrystal to avoid such tactics if they put civilians at risk.

On Friday, a NATO spokesperson said fuel tankers are often used in suicide attacks, which partially prompted the German military to call in the U.S. jet.

McChrystal has already met with Afghan leaders, including President Hamid Karzai, to offer condolences for the civilian casualties, and said civilian lives should not be sacrificed in the fight against the Taliban.

"I am here today to ensure that we are operating in a way that is truly protecting the Afghan people from all threats," McChrystal said.

One local official called for more air strikes, saying they could help push militants from the region.

"If we did three more operations like we did yesterday morning, the Kunduz situation would be peaceful and stable," said Ahmadullah Wardak, a provincial council chief.

At a meeting with senior NATO commanders, McChrystal said "we need to know what we are hitting," according to an unnamed aide.

A 10-member team of NATO investigators, led by U.S. Rear Admiral Gregory J. Smith, flew over Kunduz province Saturday and spoke to two wounded villagers at a nearby hospital.

German officials from the nearby base estimated that 57 militants were killed in the air strike and said no civilians were believed to be in the area at the time.

German Defence Minister Franz Josef Jung told a weekly newspaper Saturday that officials were not aware of any civilian deaths.

"Based on the information I have at this time, only Taliban terrorists were killed in the strikes carried out by U.S. aircraft," Jung was quoted as saying in Bild am Sonntag.

However, NATO Secretary General Anders Fogh Rasmussen acknowledged some civilian deaths. And Peter Galbraith, the deputy UN representative to Afghanistan, said Saturday he was "very concerned" about possible civilian deaths.

"Steps must also be taken to examine what happened and why an air strike was employed in circumstances where it was hard to determine with certainty that civilians were not present," Galbraith said.

Mohammad Yawar, a local government spokesperson, estimated that more than 70 people were killed, at least 45 of them militants, while the local governor estimated 72 dead -- 30 of them militants -- and 15 wounded.

Ten-year-old Mohammad Shafi was taken to Kabul for treatment after suffering injuries to an arm and a leg. He told The Associated Press that his father warned him against going near the tankers.

"While I was going to get the fuel, on the way I heard a big bang, and after that I don't know what happened," he said.

Many victims were burned beyond recognition. Villagers buried some of the dead in a mass grave.

Violence rocked the region again Saturday, when a German military convoy was hit by a bomb blast, damaging one vehicle and wounding four troops.

Abdullah Razaq Yaqoobi, police chief of Kunduz province, blamed the explosion on a suicide car bomb. However, German military officials said it was a roadside bomb.

NATO officials also confirmed that two U.S. service members were killed in Afghanistan on Saturday. One was killed after coming under fire in eastern Afghanistan, while another was killed by enemy fire in the west.

Poland's Defence Ministry also announced Saturday that one Polish soldier was killed and five others wounded when their armoured vehicle was hit by a roadside bomb.

With files from The Associated Press