The military's statement said that fighters attacked a US-led patrol that was moving through the Shah Wali Kot region of Kandahar.
"Civilians reportedly attempted to leave the area, but the insurgents forced them to remain," the US military said, but did not specify where the report was from.
Hamid Karzai, the Afghan president, condemned the killings on Wednesday, saying that 40 people had been killed and 28 wounded as a result of the air raid.
Amid the controversy over the raid in Shah Wali Kot, Afghan officials said on Thursday that seven civilians were killed in another air raid by foreign forces in the northwest of the country.
Roozben Khan, the father of the bride at the wedding ceremony in Shah Wali Kot, said that he had lost six relatives in the attack.
"I lost two sons, two grandsons, a nephew, my mother and a cousin," Khan said.
His daughter was among seven of his relatives who were wounded. The groom survived but his father, mother and sister were killed, he said.
US officials said that an investigation was under way.
Major John Redfield, a spokesperson for the US forces in Afghanistan, told Al Jazeera from Kabul: "This is an issue we take very seriously, we go to great lengths to prevent any civilian casualties but the Taliban often operate from civilian areas and sometimes draw fire there.
"But we are going to investigate this."
Redfield said that a joint investigation would be made with the Kandahar governors office, the national directorate of security and the regional police office."
Concerning the use of air strikes, he said: "We have to use any means possible against an enemy like the Taliban. We take great measures to ensure that areas are free of civilians."
The international forces in Afghanistan regularly say that Taliban fighters do little to try to protect non-combatants, but this has done little to ease growing anger in Afghanistan over civilian casualties.
The US air raid is the latest in a string of incidents in which the US military has been accused of attacking civilians.
In one of the most serious cases of civilian deaths in Afghanistan, an Afghan government commission found that a US operation in August in western Afghanistan killed some 90 civilians.
The US at first denied that any civilians had been killed, but after two investigations and the emergence of photographic evidence of dozens of bodies - including children - the US said that 33 civilians had died.
Latest air raid
While Taliban fighters are mounting a strong resurgence in Kandahar, foreign and Afghan forces are also engaged in a battle with opposition fighters in northwest Afghanistan.
Wednesday's air raid by foreign forces in the Ghormach district of Badghis province came after Taliban fighters launched an attack, provincial officials said on Thursday.
District chief Abdullah said seven civilians and 15 opposition fighters were killed in the raid.
"I myself have been to the area and seen the bodies of seven civilians. The house of a member of the provincial council was also bombed, two of his sons and a grandson were also killed," Abdullah, who only uses one name, said.
The claims of civilian deaths from the air raid by foreign forces have not been independently verified due to the remoteness of the area and its poor security.