NATO carried out its most forceful attacks in weeks in Libya on Tuesday, part of an apparently coordinated push with rebel forces to bring an end to Moammar Gaddafi’s 41-year-long rule.

NATO warplanes pummeled command-and-control targets in four cities, including Tripoli and Gaddafi’s home town of Sirte. U.S. officials said NATO had increased the tempo of its airstrikes throughout the country, and members of the alliance spoke of improved targeting of dug-in loyalist forces, made possible in part by the presence of U.S. Predator drone aircraft.

The new assault appeared to reflect increased cooperation between NATO and the rebel army, allowing the rebels to make modest gains on the ground this week, particularly in and around the western city of Misurata. Although it was too early to tell whether the advances would mark a meaningful turning point in a conflict that has left the country divided since February, the progress “shows where the momentum lies,” said a European diplomat privy to NATO’s internal discussions.

“It is noteworthy that Gaddafi’s forces have not been able to mount a sustained attack for quite some time,” said the official, who spoke on the condition of anonymity to discuss ongoing military operations. He said the rebels’ recent success in Misurata was largely due to the fact that government troops had been forced to abandon entrenched positions, making them vulnerable to ground attack.

The official also stressed the importance of Tuesday’s NATO bombings in Tripoli. Several alliance members, eager to avoid a protracted stalemate in Libya, have been pushing NATO to be more aggressive in striking Gaddafi’s center of power, despite concerns about possible civilian casualties.

NATO’s mission in Libya is to prevent civilian deaths, and alliance officials have denied targeting Gaddafi. But they bombed his compound just over a week ago, apparently killing one of his sons and three grandchildren. Gaddafi, who has refused to yield power despite massive pressure both internally and internationally, has not been seen in public since that attack.

Analysts said Tuesday that they suspected NATO’s stepped-up campaign arose from a feeling that the West needs to intervene more forcefully and cannot rely on the rebels to oust Gaddafi.

“I have no doubt the regime is crumbling to some extent,” said Tarik Yousef, dean of the Dubai School of Government and a former professor at Georgetown University. “There is a lot of circumstantial evidence that a scenario is being worked on that doesn’t involve the rebels marching to Tripoli.”

Even without rebel troops anywhere near the capital, Gaddafi’s government is struggling to maintain consistent supplies. In Tripoli and all along the route to the border with Tunisia, gas lines stretch in some cases for more than half a mile, testimony to terrible shortages brought on by strict international sanctions. Many Libyans say they have to camp out in their cars for a week to fill their tanks — or face paying 30 times the official government rate on the black market.

Command and control

The NATO attacks on Tripoli occurred early Tuesday morning. Jets could be heard booming over the city; several large explosions followed. NATO said its airstrikes also hit targets in Mizdah, a town 114 miles south of Tripoli; Sirte, a Gaddafi stronghold on the Gulf of Sidra; and Misurata.

The Libyan government took journalists early Tuesday to a hospital in central Tripoli that was next door to an intelligence building that was hit by the attacks.

NATO officials insisted that all the strikes — including the ones in Tripoli — were aimed at military targets and were in line with U.N. mandates limiting military action to protecting civilians.

“What we can do is to protect civilians by taking out major parts of the Gaddafi war machine,” NATO Secretary General Anders Fogh Rasmussen said in an interview with the Atlanta Journal Constitution and NPR during a visit to Atlanta. “So, we target critical military capabilities, like tanks and armored vehicles, rocket launchers, ammunition depots, command-and-control centers, and other facilities that can be used to attack the civilian population.”

NATO confirmed Tuesday that Predator drones had teamed up with British fighter jets in an attack earlier in the week on a Misurata building that was being used by Gaddafi forces to direct artillery and rocket fire. One of the unmanned planes conducted surveillance of the building and helped guide a pair of Royal Air Force Tornados to the site. The jets fired missiles that knocked out the building’s upper floors, where the loyalists’ spotters were operating, an alliance spokesman said.

Still, residents said conditions in Misurata, the closest rebel outpost to the capital, remain miserable.

“You still can see a queue of people looking for food, looking for bread. We’ve run out of our medication, and you cannot find vegetables anywhere,” said Aiman, a doctor at the main hospital in Misurata, who asked that only his first name be used because he was concerned about his safety. “Before we think about Tripoli, we have to secure Misurata.”

Rebels fighting in eastern Libya have been bogged down for weeks, unable to capture the city of Brega, where there is a major oil terminal. Fighters in the frontline city of Ajdabiya said that in order to take Brega, the rebel army needs more weapons.

“We ask the governments of all the Western countries to help us. We ask for more weapons for fighting at the front line,” said a commander at Ajdabiya’s western entrance, Abduljawad al-Badeen.

But Badeen said the rebels had recently procured arms from military units that had defected and from abandoned army depots in eastern Libya, giving them access to antitank missiles, rocket launchers and machine guns. “Before, we were fighting with different weapons. Gaddafi had much more,” he explained. “But now we are much more evenly matched.”

Warrick reported from Washington. Special correspondent Portia Walker in Benghazi, Libya, and correspondent Simon Denyer in New Delhi contributed to this report.