French warplanes have hit four tanks used by forces loyal to Muammar Gaddafi on the outskirts of the opposition stronghold of Benghazi, on a day when opposition fighters in the city reported coming under constant artillery and mortar fire.
The US has also launched cruise missiles from ships based in the Mediterranean Sea, and has taken the lead in military operations during the first phase, Kimberly Halkett, Al Jazeera's correspondent in Washington DC reported.
The action marks the first international military moves against the Libyan leader, and it comes a day after the UN Security Council authorized a no-fly zone over the North African country.
In the first phase of the operation, named "Odyssey Dawn", the US will target Libyan Integrated Missile Defense Systems, mainly near Tripoli and Misurata, officials said. French aircraft had initiated operations by targeting Libyan air fields.
It is not clear when the second wave of operations will begin, but Al Jazeera's Halkett reported that it would target Gaddafi's ground forces and tanks.
Other countries involved in military operations at this stage include Canada, the United Kingdom, France and Italy.
A spokesman for the French military had confirmed that his country's fighter jets have attacked another vehicle belonging to Gaddafi's forces.
"The vehicle was clearly identified as being enemy," army spokesman Colonel Thierry Burckhard said after the first UN-mandated air strike, describing the target as "a vehicle that was threatening the civilian population".
Alain Juppe, the French foreign minister, said that operations "will continue over the next few days" until the Gaddafi government complies with UN Resolution 1973.
Libyan state television reported that civilian targets in Tripoli had been bombarded, as well as fuel stores in Misurata. The state news agency reported that there had been "civilian casualties as a result of this aggression".
The US says that no coalition military operations are currently planned for near the opposition stronghold of Benghazi, but that a no-fly zone will include Tripoli, Sabha, Natoura, Misurata and Benghazi.
Earlier on Saturday, pro-government forces had entered the western outskirts of the city, while French Rafale and Mirage fighter jets began reconnaissance overflights of "all Libyan territory".
Ahmad Shabani, a spokesman for the Libyan opposition's national council, told Al Jazeera the opposition was heartened by the move.
"We are very happy about that, hopefully it's not late... and hopefully it makes a difference," he said.
Witnesses in Bengazi, in the east of the country, said they heard large explosions on Saturday. Al Jazeera's correspondents in the city reported multiple explosions, plumes of smoke in the sky and a fighter jet belonging to the opposition getting shot down.
Government troops reportedly bombed the southern Benghazi suburb of Goreshi among other places. Artillery and mortars were also fired in the centre of the city.
Mustafa Abdel Jalil, head of the opposition National Libyan Council, told Al Jazeera "there is a bombardment by artillery and rockets on all districts of Benghazi".
James Bays, Al Jazeera''s correspondent in Benghazi, reported that while the air strikes by international planes were not evident, people were "cheered" by the report. He said, however, that there was a prevalent atmosphere of nervousness and fear, as well.
PHOTO CAPTION
A poster of Libya's leader Muammar Gaddafi, one of several which were distributed among a crowd gathered to view a burning fuel truck, is held in front of the media in Tripoli March 2, 2011.
Al-Jazeera