U.S.-led forces in Afghanistan say Friday they inadvertently killed four women and a child while battling militants in central Afghanistan.

A U.S. military spokeswoman, Lieutenant Colonel Rumi Nelson-Green, says the civilians were killed Thursday as troops moved in on a key Taliban militant in the Giro district of central Ghazni province.

She says armed militants threatened coalition forces, which responded with small-arms fire, killing several Taliban as well as the women and the child.  Three militants were arrested.

The U.S. military called the deaths "inadvertent" and promised a full investigation.

About 2,500 people, including civilians, have been killed so far this year during fighting between coalition forces and militants.

Meanwhile, officials say a coalition soldier died Friday in western Afghanistan when his convoy was hit by a bomb.

More than 500 U.S. troops have been killed in Afghanistan since 2001, when the U.S. military helped oust the Taliban-led government.

Pentagon officials say U.S. Defense Secretary Robert Gates has endorsed a $20-billion plan that would nearly double the size of the Afghan army to 120,000 troops over the next five years.  The plan also gives U.S. Army General David McKiernan broader control over U.S. forces in Afghanistan.

General McKiernan currently commands 45,000 troops in the NATO-led coalition serving in Afghanistan.  The proposal would also give him control of 19,000 U.S. troops serving outside of NATO.

Some information for this report was provided by AFP, AP and Reuters.