<CNN

"(CNN) -- Two U.S. troops were killed and 20 others wounded when a U.S. B-52 bomber missed its target north of Kandahar, Afghanistan, U.S. military officials said Wednesday.

The officials said an "unknown" number of Afghan opposition forces were killed.

Pentagon sources said the bomb involved was a JDAM (Joint Direct Attack Munition), a single 2,000-pound satellite-guided bomb.

According to defense sources, those on the ground were receiving mortar fire from Taliban positions, so U.S. commanders called in close air support. Defense sources theorized the wrong coordinates were given, the wrong coordinates were entered on the plane, or the system malfunctioned. "