Tripoli, Libya (CNN) -- Over the past few days, anti-Gadhafi forces have made "significant advances" -- in the northwest and in the regions of Misrata and al-Brega -- a spokesman for NATO's military operation told reporters Tuesday.
"Anti-Gadhafi forces are now assuming control of the key approaches to Tripoli," said Col. Roland Lavoie, who described the advances as "the most significant anti-Gadhafi territorial gain we have seen in months."
Since the end of July, as the threat from pro-Gadhafi forces has diminished, thousands of people have returned to their homes in the western Nafusa mountains, he said.
Since Friday, the northwest coastal city of Misrata has been free of pro-Gadhafi forces, he said. And the threat from nearby Zlitan has diminished as pro-Gadhafi forces are being pushed farther west, he added.
Over the last week, NATO warplanes have damaged or destroyed some 150 military targets as part of Operation Unified Protector, Lavoie said.
"Our assessment, without going into details, is that the Gadhafi regime does not have anymore an effective operational capability," he said.
Lavoie said that rebels had occupied Surman and Sabratha west of Tripoli, but added that the regions were "still contested."
However, Libyan state television reported that pro-Gadhafi forces and tribal fighters were "cleansing the city of Sabratha from the gangs of traitors" and had secured the coastal road, a key supply pipeline into Tripoli.
Though the center of Zawiya was under rebel control, "there's still reports of fighting also in the suburbs," Lavoie said.
Still, U.S. Secretary of State Hillary Clinton expressed optimism. "I think the sense is that Gadhafi's days are numbered," she told reporters in Washington.
But a spokesman for the Gadhafi government offered a different view. "We are doing very well," Ibrahim Musa told reporters. "It's true that it's a bit slow -- people are still saying that we're not acting immediately and that we're having problems in Surman and Sabratha and whatnot because of armed gangs. That's true but, God willing, we are able to lead this battle successfully. We will achieve peace and victory."
He added, "We are fighting NATO -- not the tens or hundreds of armed gang members. Our war is with the crusaders."
If rebels gain control of Zawiya, that would be a major stride in putting a stranglehold on the Gadhafi-controlled seat of power.
"We will be very careful entering Tripoli, which we hope to do by the end of this month," said Col. Ahmed Banni, military spokesman for the opposition National Transitional Council.
Banni said there is intelligence that some Gadhafi forces are moving to Tripoli from other fronts -- Terhouna in the southeast and Sirte farther east.
He said those forces have taken off their uniforms to blend in with the population, a "dangerous" sign those troops are preparing for a "bloody war."
He said rebels in Tripoli recently were supplied with arms. But, he said, "We asked them to stay put until the zero hour."
Col. Jumma Ibrahim, a spokesman for the rebels' western command, said Gadhafi forces controlled most of the eastern part of the city and were shelling rebels with Grad missiles and artillery.
"There are still skirmishes with the brigades in the city center, with snipers taking positions," Col. Ibrahim said. "The fight is now urban warfare there at the moment. There have been a lot injured among our ranks but it is hard to give a number."
The rebels claim control of towns west of Zawiya to near Ras Jedeir. These include Surman and Subratha.
"It is a huge deal and a decisive defeat for his forces in that region. All these areas are liberated," Banni said.
Col. Ibrahim said Garyan, south of Tripoli's city center, had been taken by rebels but Gadhafi loyalists were shelling them from a nearby town.
There has been "fierce fighting" in Terhouna. He said rebel forces were surrounding Zlitan in the south, east and northeast and fighting Gadhafi forces.
He said there's been fighting in the industrial area of al-Brega, where rebels control the residential areas except for one controlled by the Gadhafi government.
Gadhafi forces also control the industrial area, Banni said.
"He is trying his hardest to prevent us from access to $35 million worth of daily oil money under normal circumstances in al-Brega," Banni said. "If we control the port and the refinery in the industrial area, we'd have that money."
CNN's Amir Ahmed, Jomana Karadsheh, Kareem Khadder and Matthew Chance contributed to this report.