Kabul  - One Afghan schoolchild was killed and three US soldiers and 49 Afghan civilians were wounded Tuesday in a blast near a US military convoy in eastern Afghanistan, officials said.

A team of US military soldiers were helping to tow a disabled military vehicle in Assadabad city, the provincial capital of the eastern province of Kunar Tuesday morning when they came under small arms fire, Brain Naranjo, a US military spokesman, told the German Press Agency dpa.

"As they were attempting to free the vehicle that had become stuck, an unknown person from a window of a nearby building threw a grenade, injuring three soldiers and a number of local citizens" he said.

Kunar Governor Sayed Fazilullah Wahidi told dpa that the blast killed a child and wounded 49 including several schoolchildren, shopkeepers and other civilians.

Mohammad Asif Nang, a spokesman for the Education Ministry in Kabul, confirmed one student was killed in the blast and 15 other students were among those wounded in the incident.

Afghan local media, citing witnesses and wounded people in the hospitals in Assadabad, said the US military forces threw hand grenades after the shots rang out.

The Afghan provincial government had assigned a team to investigate the incident, Wahidi said. Another senior police official, who did not want to be named because he was not authorized to talk to media said, "Several witnesses including policemen present at the scene told me that the US soldiers used hand grenades to open their way and escape."

But Naranjo said that US military "checked and double checked the allegations" but could not find any sign to suggest that those accusations were true.

Civilian casualties at the hands of international forces have become the main source of tension between the Afghan government and foreign forces in the country.

Tuesday's allegations of civilian casualties came a day after a Pentagon investigation found that there were "some problems with some tactics, techniques and procedures" the way US military air support was used in Farah province last month.

The Afghan government said that more than 140 civilians were killed and 25 were wounded in the US air raid in Bala Bulok district in May 4. The attack sparked an outcry in Afghanistan, prompting President Hamid Karzai to call a ban on airstrikes in residential areas.

The US military has repeatedly accused the Taliban militants of using noncombatants as human shields during their attacks against Afghan and international forces.

There are more than 70,000 foreign troops, with more than half of them US forces, stationed in Afghanistan. Around 21,000 additional US soldiers are expected to arrive in the country by summer.(dpa)