Western warplanes silenced Muammar Gaddafi's artillery and tanks besieging the rebel-held town of Misrata on Wednesday after an American admiral warned that the Libyan leader's armor was now in the cross-hairs.

Breathing defiance, Gaddafi earlier said Western powers carrying out air strikes on Libya were "a bunch of fascists who will end up in the dustbin of history."

The Western powers enforcing the U.N. resolution to protect Libyan civilians are struggling to agree on a coherent command structure including NATO after Washington said it wanted to hand over leadership of the campaign in the coming days.

While four nights of Western airstrikes hit Libyan air defenses and an armored column in the east, Gaddafi's tanks had kept up their shelling of Misrata in the west, killing dozens of people this week. Residents said a "massacre" was taking place with doctors treating the wounded in hospital corridors. Government snipers killed 16 people on Wednesday, rebels said.

"Now with the air strikes we are more optimistic," Saadoun, a Misrata resident, told Reuters by telephone. "These strikes give us hope, especially the fact they are precise and are targeting the (Gaddafi) forces and not only the bases."

"Before the strikes, tanks shelled the city ... but now they haven't fired a single artillery (round) since the air strike."

Such precision bombing missions can be directed at long distance with electronic systems and sometimes use rebel agents in the target zone or special forces long-range reconnaissance patrols who guide the warplanes in.

At least two explosions were heard in the Libyan capital Tripoli before dawn on Wednesday and Gaddafi looked set to dig in for the long haul.

"We will not surrender," Gaddafi told supporters forming a human shield to protect him at his Tripoli compound, which came under attack in 1986 from the Reagan administration and once again in the current round of air raids.

There were no reports of civilian casualties caused by Western airstrikes, said Rear Admiral Gerard Hueber, a top U.S. military officer involved in enforcing the no-fly zone. But neither had Libyan forces pulled back from Misrata, he said.

"There have been no reports of civilian casualties. Our mission here is to protect the civilian populace and we choose our targets and plan our actions with that as a top priority," he told reporters by phone from the command ship USS Mount Whitney in the Mediterranean.

Prior to the Misrata strikes, U.S. Rear Admiral Peg Klein said warplanes, which had been suppressing Libya's air defenses, would now be sent out to attack Gaddafi's tanks.

GADDAFI'S TANKS ARE TARGETS

"Some of those cities still have tanks advancing on them to attack the Libyan people," said Klein, commander of the expeditionary strike group aboard the USS Kearsarge off Libya.

"We are authorized, and the president made the nexus between the Security Council resolution and what he considers our legal mandate to attack those tanks. So that is the type of target that our strike aircraft will go at."

British Air Vice Marshal Greg Bagwell said on Wednesday at a base in Italy that Western forces had destroyed Libya's air force and were flying with impunity across its air space, attacking ground troops wherever they threatened civilians.

The allies had flown 175 sorties in the last 24 hours, with the U.S. flying 113 of those, Hueber said.

The siege of Misrata, now weeks old, had become increasingly desperate, with water cut off for days and food running out, doctors operating on patients in hospital corridors and many of the wounded left untreated or simply turned away.

The air strikes did not stop the snipers.

"The snipers are ... shooting at the hospital and its two entrances are under heavy attack. No one can get in or out," said Saadoun.

It was impossible to independently verify the report.

The Libyan government denies its army is conducting any offensive operations and says troops are only defending themselves when they come under attack.

Gaddafi forces resumed their bombardment of Zintan, another rebel-held town in west Libya, a resident said, and tanks were expected there.

"Gaddafi's brigades started bombardment from the northern area half an hour ago. The bombardment is taking place now. The town is completely surrounded. The situation is very bad," the resident, Abdulrahman, told Reuters by telephone from the town.

"They are getting reinforcements. Troops backed with tanks and vehicles are coming. We appeal to the allied forces to come and protect civilians," he said. Six people were killed in the bombardment, a rebel spokesman said.

REBELS FIGHT TO BREAK IMPASSE

In the east of this oil-producing north African desert state, disorganized and badly equipped rebels fighting to end Gaddafi's 41-year rule have failed to capitalize on foreign air strikes and have been pinned down outside Ajdabiyah, 150 km (90 miles) west of Benghazi.

Rebels were clashing with the army inside Ajdabiyah, rebel fighters said on Wednesday, and residents were fleeing.

Fighters said some groups had made covert forays into the town through the desert but that tanks at the town entrance had kept their main force at bay.

"We went into Ajdabiyah yesterday (Tuesday) at 2 p.m. It's not Ajdabiyah anymore," said rebel fighter Faraj Ali, in his machinegun-mounted truck. "It's dead, destroyed, a ghost town."

A family leaving Ajdabiyah said a fraction of the residents remained. "I saw bodies in the streets, and buried and washed some myself as they're rotting in the morgue. There's not been electricity for a week," said one man, declining to be named.

Missiles landed near rebel positions on Wednesday and shelling in previous days killed a number of rebel fighters.

Fighter Ali despaired of what he saw as inertia by the leadership in Benghazi and called for more help from the West.

"The National Libyan Council aren't the people to ask for anything to be frank. We want help from the West. If it weren't for them, Gaddafi's forces would be in Benghazi," Ali said.

As the rebels sought to organize their command structure on the battlefield, the rebel political leadership named Mahmoud Jabril to head an interim government and pick ministers.

Jabril, a reformer who was once involved in a project to establish a democratic state in Libya, is already the head of a crisis committee to cover military and foreign affairs.

Council members were in Paris on Wednesday, and gave assurances a secular democracy would respect all oil contracts.

NATO TO COORDINATE

The United States, with its forces already tied up in Iraq and Afghanistan, has said it wants to take a back seat.

French Foreign Minister Alain Juppe said NATO would take on a coordination role in the Libya intervention and a contact group would be formed, made up of representatives of coalition countries, African Union, Arab League and EU countries, which will be in charge of strategic planning.

The group is to meet in London next Tuesday, Britain said.

The United States, Britain and France agreed on Tuesday that the alliance should play a key operational role, but the assent of all 28 NATO states is needed and they have been split over whether it should also exercise political control.