The US, Britain and France pounded Libya with Tomahawk missiles and air strikes into the early hours of Sunday, sparking fury from Moamer Kadhafi who said the Mediterranean was now a "battlefield."
US and British forces fired at least 110 Tomahawk cruise missiles at Libya's air defence sites on Saturday, a top US military officer said, two days after a UN Security Council resolution with Arab backing authorized military action.
An AFP correspondent said bombs were dropped early Sunday near Bab al-Aziziyah, the Tripoli headquarters of strongman Moamer Kadhafi, prompting barrages of anti-aircraft fire from Libyan forces.
State television had earlier said hundreds of people had gathered to serve as human shields at Bab al-Aziziyah and at the capital's international airport.
A Libyan official told AFP that at least 48 people had died in the assaults, which began with a strike at 1645 GMT Saturday by a French warplane on a vehicle the French military said belonged to pro-Kadhafi forces.
Libyan state media said that Western warplanes bombed civilian targets in Tripoli, causing casualties while an army spokesman said strikes also hit fuel tanks feeding the rebel-held city of Misrata, east of Tripoli.
Kadhafi, in a brief audio message broadcast on state television, fiercely denounced the attacks as a "barbaric, unjustified Crusaders' aggression."
He vowed retaliatory strikes on military and civilian targets in the Mediterranean, which he said had been turned into a "real battlefield."
"Now the arms depots have been opened and all the Libyan people are being armed," to fight against Western forces, the veteran leader warned.
Libya's foreign ministry said that in the wake of the attacks, it regarded as invalid a UN resolution ordering a ceasefire by its forces and demanded an urgent meeting of the Security Council.
The attacks on Libya "threatens international peace and security," the foreign ministry said in a statement.
"Libya demands an urgent meeting of the UN Security Council after the French-American-British aggression against Libya, an independent state member of the United Nations," the statement said.
On Thursday, the Security Council passed Resolution 1973, which authorized the use of "all necessary means" to protect civilians and enforce a ceasefire and no-fly zone against strongman Moamer Kadhafi's forces.
The following day, Libya declared a ceasefire in its battle to crush an armed revolt against Kadhafi's regime which began on February 15 and said it had grounded its warplanes.
As a result of the Western attacks, however, "the effect of resolution 1973 imposing a no-fly zone are over," the ministry statement said.
State television, quoting a security official, said Libya had also decided to suspend cooperation with Europe in the fight against illegal immigration due to the attacks.
"Libya has decided not to be responsible over the illegal immigration to Europe," the television cited the official as saying.
Boats carrying thousands of undocumented migrants, mainly Tunisians, have landed on the Italian island of Lampedusa in recent weeks putting a heavy strain on Italy's immigration infrastructure.
US President Barack Obama, on a visit to Brazil, said he had given the green light for the operation, which is codenamed "Odyssey Dawn."
"Today, I authorized the armed forces of the United States to begin a limited military action in Libya," Obama said in Brasilia.
But with nearly 100,000 US troops fighting a protracted war in Afghanistan and with Saturday's missile strikes coming eight years to the day after the United States launched its war in Iraq -- Obama made clear that operation "Odyssey Dawn" would not send US troops to Libya.
"As I said yesterday, we will not I repeat we will not deploy any US troops on the ground," he said.
The first Tomahawk missile struck at 1900 GMT on Saturday following air strikes carried out earlier by French warplanes, Admiral William Gortney, director of the US joint staff, said in Washington.
"It's a first phase of a multi-phase operation" to enforce the UN resolution and prevent the Libyan regime from using force "against its own people," he said.
One British submarine joined with other US ships and submarines in the missile attacks, he said.
The first strikes took place near Libya's coast, notably around Tripoli and Misrata, "because that's where the integrated missile defence systems are."
The targets included surface-to-air missile sites but it was too early to say how effective the Tomahawk strikes were, he said.
"Because it is night over there, it will be some time before we have a complete picture of the success of these strikes," the admiral said.
Russia's foreign ministry expressed regret over the attacks under a Security Council Resolution 1973 which was "adopted in haste," while the African Union, which opposed military action, aims to send a delegation to Tripoli on Sunday.
But British Prime Minister David Cameron said he held Kadhafi responsible for the situation in his country and that "the time for action" by the international community had come.
"Colonel Kadhafi has made this happen. He has lied to the international community, he has promised a ceasefire, he has broken that ceasefire. He continues to brutalize his own people," Cameron told British television.
In the rebel camp, celebratory gunfire and honking of car horns broke out in Al-Marj, 100 kilometers (60 miles) from Benghazi, to welcome the start of military operations against Kadhafi, correspondents said.
Thousands earlier Saturday fled Benghazi as Kadhafi loyalists pounded the eastern city, the rebels' stronghold, with shells and tank fire after two early morning air strikes.
Since Friday, the Libyan government has insisted it was observing a self-declared ceasefire. It said its armed forces had come under attack on Saturday west of Benghazi, including by rebel aircraft, and had responded in self-defence.
But the rebels, who have been trying to overthrow the Libyan leader for more than a month, said government troops had continued to bombard cities, violating the ceasefire continuously.