Tripoli: Muammar Gaddafi's 42-year rule in Libya is "crumbling," the NATO military alliance claimed Monday as rebels launched a fierce street battle for Tripoli in a final push for victory.

"What we're seeing Monday night is the regime crumbling," chief NATO spokeswoman Oana Lungescu told a news agency about the final push for victory in the capital."The sooner Gaddafi realizes there is no way he can win, the better for everyone.

"What you are seeing Monday night is the cumulative effect, over time, of the eroded capabilities of the regime, "Lungescu said, citing more than 4,000 military targets damaged or destroyed in the last four months.

"Clearly we're into the last stage of the regime – the writing is on the wall.

" We' are seeing people packing their bags three top people defecting in the last couple of days, and Gaddafi-controlled territory shrinking before our eyes."

After rebels claimed "coordinated" action during the capture of a key forest staging post on the road to Tripoli, Lungescu insisted NATO was not actively providing "cover fire" for the rebels -- but forces were being scrambled to leap to their defiance during resistance.

"We are not taking part in any formal coordination on the ground," she maintained. "That's not the mandate we're not there to provide immediate assistance, or cover, if you like, yes.

"Obviously, though, we do track what's happening on the ground -- and if we see tanks or other equipment going out to attack, we fire," she said of the rebels' aerial umbrella.

Advocacy group Human Rights Watch said earlier it has sent investigators into regime-controlled territory and "visited sites of NATO airstrikes where civilians are alleged to have died."