The NATO military alliance has endangered its credibility with a bomb that destroyed a house in the Libyan capital, killing several residents, Italy's foreign minister said on Monday.
It was the first time NATO 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 said the intended target was a missile site. The head of its Libya operations said he regretted the loss of life and that a system failure may have knocked the weapon off course.
Libyan officials accused NATO of deliberately targeting the population and blamed the alliance for further civilian deaths in the southern town of Sebha and in Surman west of Tripoli.
"NATO is endangering its credibility; we cannot risk killing civilians," Italian Foreign Minister Franco Frattini told reporters 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 (45 miles) 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."