NATO says it regrets its first civilian casualties in Libya and its second misfire in 24 hours, as strains emerged within the alliance and rebel forces failed to make progress on the ground.
In a statement, the alliance acknowledged responsibility for civilian deaths in a Tripoli bombing raid that left nine dead, including two toddlers.
"NATO regrets the loss of innocent civilian lives," said Libyan mission commander Lieutenant-General Charles Bouchard.
"Although we are still determining the specifics of this event, indications are that a weapons system failure may have caused this incident," he added.
These first established civilian deaths come as an embarrassment for the alliance whose bombing campaign under a UN mandate is to protect civilians.
The incident also comes a day after NATO said its aircraft mistakenly hit a Libyan rebel column in the area of Brega on June 16, one of several misfires against opposition forces.
After investigating claims of civilian deaths early on Sunday by the Gaddafi regime, NATO said it appeared a weapon had failed to strike its intended target.
Journalists had been taken to the Al-Arada district of Tripoli in the dead of night, to see rescue teams and bystanders desperately searching for survivors among the wreckage of a two-storey block of flats.
An AFP correspondent saw two bodies pulled from the rubble.
Press were then taken to a Tripoli hospital and shown the bodies of a woman and two toddlers who officials said were members of the same family and had died in the raid.
Government spokesman Mussa Ibrahim said four passers-by were also killed, bringing the death toll to nine, with 18 people were wounded.
Accusing the alliance of "deliberately targeting civilians", Ibrahim insisted there were no military targets anywhere near the residential neighbourhood of the capital that was hit.
"Every mission is planned and executed with tremendous care to avoid civilian casualties," said NATO, which has conducted 11,500 sorties since it took command of the campaign three months ago.
On Saturday, NATO said that after looking into reports that an airstrike hit opposition forces in the Brega region on Thursday, "NATO can now confirm that the vehicles hit were part of an opposition patrol".
"This incident occurred in an area of conflict between (Muammar) Gaddafi forces and opposition forces," a statement added.
"We regret any possible loss of life or injuries caused by this unfortunate incident," NATO said.
The statement said a column of military vehicles including tanks was observed in an area where Libyan strongman Gaddafi's forces had recently been operating.
Four months after the start of the Libyan uprising, Gaddafi has not loosened his grip on power despite his diplomatic isolation and the NATO campaign.
Insurgents in the eastern desert have not advanced an inch for weeks while the Western alliance is beginning to show signs of strain, with Norway already announcing an end to its participation and criticism mounting in the United States.
