* Heavy firing and explosions heard in Benghazi
* Arab League chief warns on civilian casualties
* U.S. says air defences destroyed, no Libyan planes flying
* Libyan armed forces say they have ordered a ceasefire
(Recasts with fighting in Benghazi, US military briefing)
By Maria Golovnina and Michael Georgy
TRIPOLI, March 20 (Reuters) - Western powers pressed ahead on Sunday with a campaign of air attacks in Libya, promising more strikes despite criticism by the Arab League.
U.S. military officials said Saturday’s strikes had halted an advance by Muammar Gaddafi’s forces on the eastern rebel stronghold Benghazi and hit his air defences, allowing western powers to send in planes to impose a no-fly zone.
But the day-old U.N.-mandated military intervention to force Gaddafi’s troops to end attacks on civilians hit a diplomatic setback when the Arab League chief questioned the bombardment.
“What is happening in Libya differs from the aim of imposing a no-fly zone, and what we want is the protection of civilians and not the bombardment of more civilians,” Egypt’s state news agency quoted Arab League Secretary-General Amr Moussa as saying.
Gaddafi himself said the air strikes amounted to terrorism and vowed to fight to the death, although at 9 p.m. (1900 GMT) on Sunday an armed forces spokesman said the army was ordering all troops to cease fire immediately.
The United States and Britain, who along with France, Italy and Canada have joined operation “Odyssey Dawn”, dismissed the ceasefire announcement, arguing that Gaddafi’s government had promised and then broken a ceasefire on Friday.
In central Benghazi, sporadic explosions and heavy firing could be heard in the streets late in the evening. A Reuters witness said the firing lasted about 40 minutes.
Residents had said they feared some of Gaddafi’s troops could try to force their way into the city, where they would be surrounded by civilians and protected from attacks from the air.
Outside Benghazi, the advance by Gaddafi’s troops was stopped in its tracks, with smouldering, shattered tanks and troop carriers littering the main road. The charred bodies of at least 14 government soldiers lay scattered in the desert.
However, government tanks did move into Misrata, the last rebel-held city in western Libya, seeking the shelter of built-up areas after a base used by Gaddafi’s forces outside was hit by Western air strikes, residents said.
Abdelbasset, a spokesman for the rebels in Misrata, told Reuters: “There is fighting between the rebels and Gaddafi’s forces. Their tanks are in the centre of Misrata ... There are so many casualties we cannot count them.”
More on Middle East unrest: [nTOPMEAST] [nLDE71O2CH]
US military leads on Libya but for how long? [nN19235888]
Libya Graphics link.reuters.com/neg68r
Map of Benghazi link.reuters.com/gyv58r
A Libyan government health official said 64 people had been killed in the Western bombardment overnight from Saturday to Sunday, but it was impossible to verify the report.
The Arab League’s Moussa called for an emergency meeting of the group of 22 states to discuss Libya. He requested a report into the bombardment, which he said had “led to the deaths and injuries of many Libyan civilians”.
Arab backing for a no-fly zone provided crucial underpinning for the passage of a U.N. Security Council resolution last week that paved the way for Western action to stop Gaddafi killing civilians as he fights an uprising against his rule.
The intervention is the biggest against an Arab country since the 2003 invasion of Iraq. Withdrawal of Arab support would make it much harder to pursue what some defence analysts say could in any case be a difficult, open-ended campaign with an uncertain outcome.
Britain and the United States rebuffed Moussa’s comments.
A senior U.S. official said a U.N. resolution endorsed by Arab states covered “all necessary measures” to protect civilians, “which we made very clear includes, but goes beyond, a no-fly zone”.
The safe enforcement of the no-fly zone required the targeting of Libya’s air defence capabilities, a British Foreign Ministry spokesman said.
A spokesman for the rebel movement criticised Moussa’s comments, telling Al Jazeera that more than 8,000 Libyans aligned with the rebel movement had been killed.
“Today, when the secretary-general spoke, I was surprised,” Abdel Hafiz Ghoga said.
“What is the mechanism that stops the extermination of the people in Libya, what is the mechanism, Mr Secretary-General? If the protection of civilians is not a humanitarian obligation, what is the mechanism that you propose to us?”
The U.S. Chairman of the Joint Chiefs of Staff, Admiral Mike Mullen, said the no-fly zone was now in place. But he told CBS television the endgame of military action was “very uncertain” and acknowledged it could end in a stalemate with Gaddafi.
Mullen said he had seen no reports of civilian casualties from the Western strikes. But Russia said there had been such casualties and called on Britain, France and the United States to halt the “non-selective use of force”.
Libyan state television showed footage from an unidentified hospital of what it called victims of the “colonial enemy”. Ten bodies were wrapped up in white and blue bed sheets, and several people were wounded, one of them badly, the television said.
The Libyan government has denied breaking a ceasefire that it announced on Friday, blaming rebels who it says are members of al Qaeda.
The armed forces spokesman announced a new ceasefire on Sunday, saying that “the Libyan armed forces ... have issued a command to all military units to safeguard an immediate ceasefire from 9 p.m. (1900 GMT) this evening”.
Both before and after he spoke, heavy anti-aircraft gunfire boomed above central Tripoli.
A senior military official said the United States expected to conduct more strikes on Libya. “This is an ongoing military operation. I fully expect more strikes,” he said.
Britain said it was taking part in a second night of coordinated strikes and had once more launched Tomahawk cruise missiles from a submarine in the Mediterranean. Italy said it also had planes in the air.
The United States, after embarking on wars in Afghanistan and Iraq, has been reluctant to take the lead in the military operation, keen to leave this to France and Britain while also assembling a large coalition to support it.
French planes fired the first shots of the intervention on Saturday, destroying tanks and armoured vehicles near Benghazi.
France sent an aircraft carrier towards Libya and its planes were over the country again on Sunday, defence officials said. Britain said its planes had targeted Libya’s air defences, mainly around the capital Tripoli.
U.S. and British warships and submarines launched 110 Tomahawk missiles on Saturday night and Sunday morning against air defences around Tripoli and Misrata, U.S. officials said.
Aircraft from other countries, including Qatar, were also moving towards Libya to participate in the operation, Mullen said. (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 and Elizabeth Pineau in Paris, Missy Ryan in Washington, Matt Spetalnick in Rio de Janeiro; Writing by Myra Macdonald; Editing by Kevin Liffey)