NATO will continue its combat air patrols over Libya until all pro-Gadhafi forces surrender or return to barracks, officials said Monday.
Moammar Gadhafi must step down immediately in order to save lives and allow for a peaceful transition, said a NATO official who could not be identified under standing rules.
NATO has demanded that all regime troops return to barracks as a condition for the airstrikes to end.
"In the meantime, NATO aircraft will continue to protect the civilian population as mandated by the United Nations," the official said.
Earlier, NATO's Secretary-General Anders Fogh Rasmussen said the regime is "clearly crumbling."
NATO will continue to monitor Gadhafi's military units and will engage them if they make any threatening moves, Fogh Rasmussen said.
NATO warplanes have flown nearly 20,000 sorties in the past five months, including about 7,500 strike attacks against Gadhafi's forces.
The jets have hit at least 40 targets in and around Tripoli in the past two days. This was the highest number on a single geographic location since the bombing started more than five months ago, officials said.
The rapid rebel advance into Tripoli offers NATO the chance to quickly bring to a conclusion a campaign that has drawn increasing international criticism and caused serious rifts within the alliance.
NATO officials deny there has been a fundamental shift in tactics in recent days to provide close air support to the advancing rebels, saying they continue to be focused on the protection of civilian populations as mandated by the U.N. Security Council.
But they acknowledge that in response to new developments, alliance bombers have been pummeling Gadhafi's troops holding defensive positions even when they were only trying to stem the progress of the rebels.
Alliance's military planners have been racing against a deadline next month, when member states must vote on a second three-month extension of the mission. The bombing campaign has been criticized as detracting resources from NATO's main mission, the 10-year war in Afghanistan.
Also in September, the U.N. General Assembly is due to debate the airstrikes, with many members critical of NATO for overstepping the original U.N. mandate in March, which only authorized a no-fly zone and the protection of civilians caught up in the civil unrest.