NATO Secretary General Anders Fogh Rasmussen says his alliance is sticking with its mission to protect the people of Libya, despite an off-target airstrike that may have claimed civilian lives in Tripoli.

In an interview from Brussels, NATO Secretary-General Anders Fogh Rasmussen admitted a weekend airstrike did stray from its intended military target in the Libyan capital.

"This very tragic accident was caused by technical problems of our weapons systems," Rasmussen told CTV's Canada AM on Monday, conveying his regrets to the victims' families.

"And obviously we deeply regret the loss of life," he added, "but we do all we can to avoid civilian casualties."

The admission comes the day after the Libyan government led foreign journalists to a damaged residential building in Tripoli, where they said nine civilians including two children had been killed by a NATO airstrike.

The reporters, whose movements in Libya are otherwise restricted by the Gadhafi regime, were later taken to a local hospital and shown the bodies of those said to have been killed in the strike.

Libyan foreign minister Abdul-Ati al-Obeidi told the journalists that another 18 people were wounded in what he called a "deliberate attack on a civilian neighbourhood."

Rasmussen brushed that suggestion aside, however, as he said NATO forces "are very careful in identifying legitimate military targets."

And they will continue with that mission, he explained, until three military objectives are met: a complete end to all attacks against civilians, the withdrawal of Gadhafi forces to their bases, and immediate and unhindered humanitarian access to people in need.

But Rasmussen refused to guess how long achieving those goals might take.

"Obviously there is no military solution solely," he said, explaining that a concurrent political process to institute democracy in Libya is necessary too.

"We have seriously degraded the military capacity of the Gadhafi regime and the combination of this military pressure and the reinforced political pressure will eventually lead to the collapse of the Gadhafi regime," he said.

"It's not a question of if, but when."

The Libyan government has claimed NATO strikes have struck numerous civilian targets including a hotel, factory and numerous vehicle. This latest admission from NATO, however, is just the third since its UN-mandated operation began at the end of April.

Last week, NATO defence ministers approved a 90-day extension, authorizing the alliance to continue its Libya operation through September.