Forces loyal to Muammar Gaddafi attacked two Libyan towns on Tuesday after a third night of air raids on Tripoli, but the Western campaign faced questions over the future of its command structure.

With anti-Gaddafi "rebels" struggling to create a command structure than can capitalise on the air strikes against Libyan tanks and air defences, Western nations have still to decide who will run the operation once Washington pulls back.

The United States will cede control of the air assault in days, President Barack Obama said, even as divisions in Europe fuelled speculation that Washington would be forced to continue leadership of air patrols to replace the initial bombardment.

"We anticipate this transition to take place in a matter of days and not in a matter of weeks," Obama, facing questions at home about the U.S. military getting bogged down in a third Muslim country, told a news conference on a visit to Chile.

A U.S. Air Force F-15E crashed in Libya overnight and one crewman had been recovered and the other was "in the process of recovery," the U.S. military said. The crash was likely caused by mechancial failure and not hostile fire, it said.

In the latest fighting on Tuesday, Gaddafi forces used tanks to shell the "rebel"-held western city of Misrata and casualties included four children killed when the car they were travelling in was hit, residents told Reuters. The death toll on Monday had reached 40, they said.

"The situation here is very bad. Tanks started shelling the town this morning," a resident, called Mohammed, told Reuters by telephone from outside the city's hospital, adding:

"Snipers are taking part in the operation too. A civilian car was destroyed killing four children on board, the oldest is aged 13 years."

Al Jazeera news network said Gaddafi forces were trying to seize the western "rebel"-held town of Zintan near the Tunisian border in an attack using heavy weapons.

Residents had already fled the town centre to seek shelter in mountain caves.

Libyan state television said several sites had come under air attack in Tripoli on Monday. There was no immediate confirmation of new air strikes by Western powers in the campaign to enforce a no-fly zone and protect civilians after an uprising against Gaddafi's 41-year rule.

"Rebels", who were driven back towards their eastern Benghazi stronghold before the air attacks halted an advance by Gaddafi forces, have done nothing to resume their planned advance on Tripoli - raising fears the war could grind to a stalemate.

But Washington, wary of being drawn into another war after long campaigns in Iraq and Afghanistan, has ruled out specific action to overthrow Gaddafi, though France said on Monday it hoped the Libyan government would collapse from within.

Obama did not spell out which nation or organisation would take charge of the campaign, but Britain and France took a lead role in pushing for air strikes in Libya which have already destroyed much of its air defences.

British Prime Minister David Cameron said the intention was to transfer command to NATO, but France said Arab countries did not want the US-led alliance in charge of the operation in the oil-producing north African desert state.

NATO officials were due to resume talks in Brussels on Tuesday after failing to reach an agreement on Monday.

Italy's Foreign Minister Franco Frattini said if agreement was not reached for NATO control of the no-fly zone over Libya, Italy would resume its own separate command structure.

A NATO role would require political support from all the 28 NATO states, and on Monday Turkish Prime Minister Tayyip Erdogan said Turkey wanted several conditions met for a NATO role.

Andrew Bacevich, a professor of international relations at Boston University, said it would be difficult to stand up a multinational command structure "on the fly."

"If that's what's being attempted then the hand-off may take longer than the Obama administration would like," he said.

Rifts are also growing in the international community over Libya, with Russian Prime Minister Vladimir Putin comparing the U.N. resolution to a call for "medieval crusades".

China and Brazil were urging a ceasefire amid fears of civilian casualties.

Libyan state television reported that several sites in Tripoli had been subject to new attacks by what it called the "crusader enemy". "These attacks are not going to scare the Libyan people," the television station said.

Anti-aircraft gunfire rang out throughout the night and pro-Gaddafi slogans echoed around the city centre. Cars sped through Tripoli streets honking wildly.

Libyan television was showing archive footage of Gaddafi being greeted by cheering crowds waving his portrait. The images were set to stirring patriotic music. Gaddafi himself has not been since in public since the air strikes began at the weekend.

State television was also broadcasting old footage of military parades, including pictures of elite troops marching in formation wearing balaclavas and gas masks.

Al Jazeera television said radar installations at two air defence bases in eastern Libya had been hit.

A Libyan government spokesman also said that 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."

These reports could not be independently verified.

The United States and its allies have run into some criticism for the intensity of the firepower unleashed on Libya, including more than 110 Tomahawk missiles on Saturday. The next step is to patrol the skies to enforce the no-fly zone.

The U.N. Security Council is far from united over Libya. In last week's vote, ten countries supported the resolution and the other five council members abstained including Russia and China, which, however, refrained from using their veto power.

Libyan "rebels" have welcomed the air strikes and say they are coordinating with the Western powers launching them.

But 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 rather only protecting civilians, as their U.N. mandate allows, leaving disorganised rebel fighters struggling to make headway.

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," Cameron said during a parliamentary debate on Libya.