NATO has admitted "a weapons systems failure" may have led to civilian casualties in Sunday morning's air strike in the Libyan capital.
In a statement, the alliance said the intended target of the strike in Tripoli was a military missile site, but "it appears that one weapon" did not hit it, the BBC reports.
The Libyan government says nine people died, including two babies, and 18 people were wounded.
NATO is enforcing a United Nations resolution to defend Libyans from pro-Gaddafi forces.
"NATO regrets the loss of innocent civilian lives and takes great care in conducting strikes against a regime determined to use violence against its own citizens," said Lieutenant General Charles Bouchard, commander of operation Unified Protector.
"Although we are still determining the specifics of this event, indications are that a weapons system failure may have caused this incident."
The statement said that more than 11,500 sorties had already been conducted and "every mission is planned and executed with tremendous care to avoid civilian casualties".
The attack, in one of Tripoli's poorer neighbourhoods, happened shortly after midnight, according to Libyan officials.
The level of damage looked like the aftermath of an air strike, with concrete floors blown out on to the street - the incident did not look like a government stunt, a BBC journalist at the scene reports.
NATO has flown more than 11,000 sorties since operations began, including nearly 4400 strike attacks against government targets across Libya.
Its mission to enforce the no-fly zone over Libya to protect civilians using "all necessary measures" short of a ground invasion began in March in response to Colonel Muammar Gaddafi's violent response to an uprising.
It was mandated by the UN, and led by France, Britain and the United States until the end of March, when NATO took over.