By Maria Golovnina and Michael Georgy
TRIPOLI (Reuters) - Anti-aircraft fire and explosions reverberated across Tripoli for a third night on Monday and state television said several sites had come under attack in the capital.
Western powers had no immediate confirmation they had launched fresh strikes on Tripoli in a campaign to target Libyan air defenses and enforce a no-fly zone.
A U.S. general said, however, that attacks on Libya -- launched in a U.N. mandated operation to stop attacks on civilians by Muammar Gaddafi's forces -- were likely to slow in the coming days.
Despite the campaign, residents in two besieged rebel-held western cities, Misrata and Zintan, said they had been attacked by government troops, some of whom were expected to try to force their way into civilian areas to escape attack from the air.
Rebels, who had been driven back toward their eastern Benghazi stronghold before the air attacks halted an advance by Gaddafi's forces, have so far done little to capitalize on the campaign, raising fears the war could grind to a stalemate.
Washington, wary of being drawn into another war after long campaigns in Iraq and Afghanistan, has ruled out specific action to overthrow Gaddafi, although France said on Monday it hoped the Libyan government would collapse from within.
"My sense is that, that unless something unusual or unexpected happens, we may see a decline in the frequency of attacks," General Carter Ham, who is leading U.S. forces in the Libyan operation, told reporters in Washington.
He added, however, that "we possess the capability to bring overwhelming combat power to bear, as we have done in the initial stages of this, where it's been required."
Libyan state television reported that several sites in Tripoli had been subjected to new attacks by what it called the "crusader enemy."
"These attacks are not going to scare the Libyan people," state television said.
Anti-aircraft gunfire rang out throughout the night and pro-Gaddafi slogans echoed around the city center. Cars sped through Tripoli streets honking wildly.
Al Jazeera television said coalition forces had struck radar installations at two air defense bases in eastern Libya late on Monday. However, a French armed forces spokesman said France, which has been involved in strikes in the east, had no planes in the air at the time.
In Misrata, residents said people had gone out into the streets to try to stop Gaddafi's forces entering the city.
"When they gathered in the center the Gaddafi forces started shooting at them with artillery and guns," said the resident, who gave his name as Saadoun. He said nine people were killed.
Zintan, near the Tunisian border, faced heavy shelling, two witnesses said, forcing residents to flee to mountain caves. Several houses were destroyed and a mosque minaret destroyed.
"New forces were sent today to besiege the city. There are now at least 40 tanks at the foothills of the mountains near Zintan," Abdulrahmane Daw told Reuters by phone from the town.
The reports could not be independently verified.
The United States has run into some criticism for the intensity of the firepower used on Libya, which included more than 110 Tomahawk missiles fired on Saturday.
Arab League chief Amr Moussa has questioned the methods used, while Russian Prime Minister Vladimir Putin compared the air campaign to "medieval crusades."
President Barack Obama said the United States, which has been joined by Britain, France, Canada and Italy among others, planned to transfer the lead military role shortly. Britain and France led calls for the intervention.
"We anticipate this transition to take place in a matter of days and not in a matter of weeks," Obama told a news conference during a visit to Chile.
Libyan rebels have welcomed the air strikes and say they are coordinating with the Western powers launching air strikes.
There was little sign at the vanguard of battle in east Libya that this communication extended to forward rebel units.
Western powers say they are not providing close air support to rebels or seeking to destroy Gaddafi's army, but only protecting civilians, as their U.N. mandate allows, leaving disorganized rebel fighters struggling to make headway.
"If we don't get more help from the West, Gaddafi's forces will eat us alive," rebel fighter Nouh Musmari told Reuters.
Security analysts say it is unclear what will happen if the Libyan leader digs in, especially since Western powers have made clear they would be unwilling to see Libya partitioned between a rebel-held east and Gaddafi-controlled west.
"There is still a real risk of a protracted stalemate, with neither side wanting to negotiate. So the endgame remains very unclear," said Jeremy Binnie, a senior analyst with IHS Jane's.
British Prime Minister David Cameron said the operation would not drag into another Iraq-style conflict.
"This is different to Iraq. This is not going into a country, knocking over its government and then owning and being responsible for everything that happens subsequently," he said during a parliamentary debate on Libya.
"This is about protecting people and giving the Libyan people a chance to shape their own destiny."
In an appearance on Libyan television on Sunday, Gaddafi promised his enemies a "long war."
GADDAFI NOT A TARGET, WEST SAYS
Officials in Tripoli said one missile on Sunday, which they said was intended to kill Gaddafi, had destroyed a building in his compound, heavily bombed in 1986 by the United States.
"It was a barbaric bombing," said government spokesman Mussa Ibrahim, showing pieces of shrapnel that he said came from the missile. "This contradicts American and Western (statements) ... that it is not their target to attack this place."
A Libyan government spokesman said foreign attacks had killed many people by bombing ports and Sirte airport.
"You saw that place (Sirte airport)," Mussa Ibrahim told a news conference. "It's a civilian airport. It was bombarded and many people were killed. Harbours were also bombarded."
Cameron said there were no plans to target Gaddafi. "The U.N. resolution is limited in its scope, it explicitly does not provide legal authority for action to bring about Gaddafi's removal from power by military means," he told parliament.
"We will help fulfill the U.N. Security Council (resolution), it is for the Libyan people to determine their government and their destiny, but our view is clear, there is no decent future for Libya with Colonel Gaddafi remaining in power."
French Foreign Minister Alain Juppe said he hoped Libyans themselves would topple Gaddafi: "When will the regime collapse? It is quite possible that, given the weakness of the regime, it will break up from within."
(Reporting by Mohammed Abbas and Angus MacSwan in Benghazi, Maria Golovnina and Michael Georgy in Tripoli, Hamid Ould Ahmed and Christian Lowe in Algiers; Tom Perry in Cairo, John Irish in Paris, Missy Ryan in Washington, Matt Spetalnick in Rio de Janeiro; Writing by Myra MacDonald; Editing by Andrew Dobbie)