Some details were still unclear, but a local Afghan official and two witnesses said that the civilians were killed Thursday afternoon when a NATO aircraft fired on a house after a firefight with Taliban militants who had attacked a NATO convoy. The Taliban were operating in Luchak, a farming village in central Helmand Province, the epicenter of the insurgency. When the convoy arrived in Luchak, about a half-dozen Taliban fighters opened fire from behind a wall next to a house.

After a 10-minute exchange of fire, the insurgents ran away, the witnesses said. Then, about 10 minutes later, a pair of helicopters appeared in the sky, the villagers said.

Maj. Michael Johnson, a NATO spokesman, said the aircraft was a plane that had come in support of the troops on the ground.

The witnesses said the aircraft fired on the house, killing five men inside. Two Afghans were wounded.

“Afterwards some of the other villagers and I went to the house and we saw a man and woman crying and screaming for the dead,” said Khair Mohammed, who lives in Luchak. “It was a very bad scene.”

Another villager, Hajji Baz Muhammad, gave a similar account, adding that the Taliban dominated Luchak and often used it to ambush NATO troops. Mr. Muhammad said that the Taliban had decreed that everyone turn off their cellphones after 6 p.m.

“The Taliban have a lot influence here,” he said.

Major Johnson said a team had been sent to the area to figure out what happened, but its report was not yet complete. He said it was likely, though, that NATO had killed the civilians. “They feel there is a fair chance that those seven causalities were caused by us,” he said.

Most NATO troops in the area are American or British.

More civilians are being killed and wounded now than at any time since the American-led war here began in 2001. The overwhelming majority of civilians are killed by insurgents, according to the United Nations and other aid groups.

Still, the issue is an extremely delicate one between the Afghan and American governments. American and other NATO commanders have sharply restricted the use of airstrikes against insurgents. In most cases, soldiers caught in a firefight may not call in airstrikes to kill insurgents who are hiding in houses in populated areas, unless the NATO soldiers are in danger of being overrun.

On Saturday, President Hamid Karzai of Afghanistan took up the matter with President Obama in an hourlong video teleconference. A statement released afterward by Mr. Karzai’s aides said he had given Mr. Obama a letter calling for a “strategic review” of NATO’s campaign, based on the “rightful demands of the people of Afghanistan that terrorism cannot be fought in Afghan villages.”

In its own statement, the American Embassy said that Mr. Obama and Mr. Karzai discussed a variety of subjects, including civilian casualties. It made no reference to Mr. Karzai’s request.

Sharifullah Sahak contributed reporting from Kabul, and an Afghan employee of The New York Times from Helmand Province.