Three U.S. Special Forces soldiers and five Afghan opposition fighters have been killed by "friendly fire" from a U.S. bomb, two Defense Department officials said.

Pentagon spokeswoman Victoria Clarke and Navy Rear Admiral John Stufflebeem told journalists at a Pentagon briefing December 5 that a 2,000-pound, precision-guided joint direct attack munition (JDAM), dropped from a B-52 bomber, exploded about 100 meters from U.S. and opposition forces engaged in a firefight with Taliban fighters north of Kandahar. Apart from the deaths, 19 U.S. soldiers -- described by Stufflebeem as Special Forces -- and an unspecified number of Afghan opposition fighters were wounded in the blast, they said.

Stufflebeem said the injured and killed U.S servicemen were members of two teams of Special Forces that had come together and had called for the air strike in support of opposition fighters during the firefight. An investigation is under way to determine why the bomb hit so close to the U.S. and opposition positions, and both officials stressed that it was too early to draw conclusions.

"You also need to appreciate that ... a close-air-support mission ... is one of the most potentially hazardous ... that we use," Stufflebeem said. "Calling in air strikes ... on enemy forces that you're engaged in close proximity to is a hazardous business and takes very fine control and coordination and precision," he added.

About 100 U.S. and coalition aircraft were flown on strike missions December 4, Stufflebeem said. Around 80 were sea-based tactical aircraft, while 12-to-14 were land-based tactical jets, and 8-to-10 were long-range bombers. They were used against four planned target areas, mostly around Kandahar and Jalalabad, he said.

Three C-17 cargo planes air-dropped 44,000 humanitarian daily rations west of Mazar-i-Sharif December 4, bringing the total number of individual food packages air-dropped to date to more than 2.187 million, Stufflebeem said. In addition, Commando Solo radio broadcasting missions were flown, while leaflets were dropped in the Jalalabad and Kandahar areas, he said.