NATO has endangered its credibility with a bomb that destroyed a house in the Libyan capital, killing several residents, Italy's foreign minister has said.
It was the first time the military alliance had acknowledged causing multiple civilian casualties in Libya and came as the alliance feels the strain of a campaign taking more time and resources than expected.
"NATO is endangering its credibility; we cannot risk killing civilians," Franco Frattini told reporters on Monday before an EU foreign ministers' meeting in Luxembourg to discuss ways to aid rebels trying to oust Muammar Gaddafi.
Frattini expressed concern that NATO was losing the propaganda war to Gaddafi and that Western media reports did not emphasise enough the good work done by the alliance every day to protect Libyan civilians.
"We cannot continue our shortcomings in the way we communicate with the public, which doesn't keep up with the daily propaganda of Gaddafi," he said.
NATO was continuing with its three-month campaign of air strikes on Monday. A Reuters reporter in central Tripoli said he heard jets overhead around midday, then a distant explosion.
There were no details immediately available on what the strike had hit.
Libyan official news agency JANA said air strikes killed four civil defence staff and wounded 10 others on Sunday when they rushed to provide first aid for people at civilian sites hit by the coalition in Sebha.
Government officials took reporters to Surman, 70km west of Tripoli, to the site of what they said was a NATO strike targeting the home of Khouildi Hamidi, a member of the 12-member Revolutionary Command Council that Gaddafi set up after seizing control of Libya in 1969.
The government said 15 civilians were killed, including three children. Government spokesman Moussa Ibrahim called the attack a "cowardly terrorist act which cannot be justified."
A statement from NATO said that a military missile site was the intended target of the raid but one of the weapons did not strike it and may have caused civilian casualties.
Speaking to Al Jazeera, Oana Lungescu, a NATO spokesperson, said NATO's killing of civilians was a "sad incident that we deeply regret".
"Basically, this is another night of murder, terror and horror in Tripoli caused by NATO," Moussa Ibrahim, a government spokesman, said at a hospital.
The most recent figures from Libya's health ministry show 856 civilians have been killed in NATO air raids since they began in March. The figure could not be independently confirmed.
Previous government-announced tolls from individual attacks have proven to be exaggerated.
Late on Saturday, NATO announced that it had mistakenly struck a column of Libyan rebel vehicles in an air attack near an eastern oil town two days earlier and expressed regret for any casualties that might have resulted.
"We are conducting operations with utmost care and precision to avoid civilian casualties. Civilian casualties figures mentioned by the Libyan regime are pure propaganda," Oana Lungescu, a NATO spokeswoman, said.
The alliance has accidentally hit rebel forces before in its air campaign to protect civilians.
The rebels have complained that NATO's raids have not helped them gain decisive momentum against the Libyan leader's better trained and equipped military.
The alliance statement gave no figures on casualties from Thursday's raid, but said it regretted "any possible loss of life or injuries caused by this unfortunate incident".
International military forces have had some trouble in hitting government troops because of their proximity to civilians. Government troops have also used civilian vehicles, making them difficult to distinguish from rebel forces.