Afghan officials say an explosion killed at least one child near a convoy of U.S. troops in eastern Afghanistan.

Authorities say the blast wounded about 50 other people in Kunar province. 

Kunar's chief of police Abdul Jalal Jalal says a grenade may have caused the explosion.

Officials say they are investigating witness reports that a U.S. soldier threw the grenade.

A spokesman for NATO-led forces in Afghanistan says initial reports indicate that an insurgent threw a grenade into the crowd.  The U.S. military said in a statement that an "unknown person from a nearby building" threw the grenade.

Monday, the U.S. Defense Department admitted that an aircraft involved in deadly air strikes last month in western Afghanistan violated rules designed to protect civilians.

Pentagon spokesman Geoff Morrell said after a briefing for Defense Secretary Robert Gates by the U.S. brigadier-general assigned to investigate the incident that there were some problems in the way the air strikes were carried out.

But he also said there is no indication that the violation resulted in civilian casualties.

The U.S. military has said between 20 and 30 civilians were killed during the battle in Farah province with insurgents.  The Afghan government has put the number as high as 140.

A major point of contention between the two countries is civilian deaths caused by U.S. air strikes on suspected militant targets.  Afghan President Hamid Karzai has said the deaths seriously undermine local support for coalition forces.

Some information for this report was provided by Reuters.