“The helicopters watched, and they thought it was a gathering and fired on it,” Mr. Abadi said. “They fired rockets. When people started to run, the helicopters’ machine guns began shooting at the people who were running.”

The American military had a different version of events, which took place in the Saha part of the Abu Dshir district. A spokesman said that earlier in the evening American forces had twice observed episodes when two or three men fired mortars into the neighborhood to the north. After the second episode, the military called for an airstrike.

“We assess possibly two or three were killed or wounded,” said Maj. Brad Leighton, a spokesman for the multinational forces in Baghdad. “We were not able to get an accurate assessment,” he added.

“Collateral damage was not observed, but it is a possibility,” Major Leighton said. “If some innocents were killed, we regret that.”

The Abu Dshir district, a district that is majority Shiite, is largely controlled by the Mahdi Army, the militia loyal to the anti-American cleric Moktada al-Sadr, according to people who live there. However, members of the Mahdi Army in Abu Dshir have been observing the cease-fire ordered by Mr. Sadr in August, neighbors said. No one in the neighborhood appeared to be armed during a reporter’s visit on Friday, although a few wore the black shirt and pants that the Mahdi Army often favors.