The official said the International Security Assistance Force (Isaf) "would probably defer in the first instance to the French authorities," in the investigation.
Bryan Whitman, a Pentagon spokesman, said: "We have no reports of any casualties caused by close air support."
Asked whether French soldiers had been killed or wounded by friendly fire, he said there were "no reports of that".
The French army has refused to comment, the AFP news agency reported.
The comments came after Nicolas Sarkozy, the French president, visited survivors of the incident at a French military base on the outskirts of Kabul on Wednesday.
He reaffirmed his government's commitment to the war in Afghanistan, saying: "We have to be here."
Speaking from Kabul, where he met Hamid Karzai, the Afghan president, Sarkozy said he had no regrets about sending 700 reinforcements to the French contingent, adding: "If it had to be done again, I would do it.
"This is where the fight against terrorism is being waged."
Al Jazeera correspondent Zeina Khodr said: "Sarkozy did not make any statements after his talks with president Karzai - just a photo op - leaving many questions unanswered.
"The main questions now: how will the loss of soldiers affect the French mission here and also Sarkozy's decision to send reinforcements as promised earlier this year."
The bodies of the 10 dead French soldiers were returned home on Wednesday as politicians and journalists questioned why France had got itself involved in the Afghan "quagmire".
"A war without end," read a headline in the Liberation newspaper, whose editorial nonetheless concluded that, for France and the 40 other nations with troops in Afghanistan, "the worst solution would obviously be withdrawal".
Francois Hollande, a Socialist party leader who had previously criticised Sarkozy's decision to send an additional 700 troops to the region, said parliament's foreign affairs and defence committee should meet.
He said: "It is a moment for contemplation ... But there also has to be a time for reflection on the sense of our presence in Afghanistan."
Sarkozy's decision in April, after heavy pressure from Nato allies, to send an extra 700 French troops to Afghanistan, to bring their number to about 3,000, was
hugely unpopular in the country.
Opinion polls showed a large majority of French opposed the move, with many fearing that France would get bogged down in an unending war whose aims were unclear or unattainable.
About 70,000 international troops, 40,000 of them with a Nato-led force, are fighting alongside Afghan security forces against Taliban fighters whose government was removed in a US-led invasion in 2001.
On Wednesday, Pierre Lellouche, the deputy of Sarkozy's right-wing UMP party, who has been tasked with writing a report on the situation in Afghanistan, said Nato's strategy "was failing, both on the political and the military level" and must be overhauled.
"Its objectives may be just, but is the strategy being used to achieve them the right one?" asked an editorial in the conservative Le Figaro daily newspaper.
"It is only by leaving behind local forces capable of containing the Taliban that Western soldiers will be able, one day, to get out of the Afghan quagmire without giving the impression that they have lost the war," it said.
"The question now," said Bruno Jeanbart of the polling institute OpinionWay, "is whether public opinion will be reinforced in its feeling of the uselessness of the French presence in Afghanistan, or will the public rally round their soldiers in difficulty, and become more favourable to it?"
The latest casualties bring to 24 the number of French troops killed in action or in accidents in Afghanistan since French soldiers were first sent there in 2002.
It was the deadliest attack on French troops since a 1983 assault in Beirut in which 58 French paratroopers serving in a UN force were killed.