NATO said on Sunday that a number of Libyan civilians were killed in a NATO airstrike in Tripoli last night due to "a weapon system failure."

"A military missile site was the intended target of air strikes in Tripoli last night. However, it appears that one weapon did not strike the intended target and that there may have been a weapons system failure which may have caused a number of civilian casualties," the military alliance said in a statement.

"NATO regrets the loss of innocent civilian lives," said Lieutenant General Charles Bouchard, commander of NATO's mission in Libya.

"Although we are still determining the specifics of this event, indications are that a weapons system failure may have caused this incident," he added.

It is the first time for NATO to acknowledge its military campaign in Libya caused civilian casualties.

Libyan Foreign Minister Abdelati Obeidi said earlier on Sunday that a NATO strike had hit a civilian house in Tripoli, killing nine residents and wounding 18 others.