Libyan leader Muammar al-Qaddafi says in a radio speech that government forces will attack the rebel stronghold of Benghazi Thursday night.
Qaddafi says his forces will retake the city, offering amnesty for those who surrender and "no mercy" for others.
"The matter has been decided ... we are coming," Qaddafi said in the radio speech.
The Libyan government said it has set a temporary cease-fire from Sunday to allow rebels to surrender, according to AFP.
It comes as the U.S. pushes for a no-fly zone and authorization for a wide range of strikes in Libya, according to the Wall Street Journal. Libya's defense minister warned on state TV that any foreign military attack would endanger air and maritime traffic in the Mediterranean, according to Reuters.
Secretary of State Hillary Clinton says the possible direct involvement of Arab nations in any international military action against Qaddafi is being discussed, according to Reuters.
Forces loyal to Libyan leader Muammar al-Qaddafi launch airstrikes against the airport in Benghazi Thursday.
Thirty people were also killed in fighting between opposition groups and Qaddafi forces in the eastern town of Ajdabiyah.
"I was at the hospital and saw 30 dead women, children and elderly men. They were all civilians not rebels," Abdel Bari Zewi, a witness, told the station, according to Reuters.
Libyan rebels shot down at least two bomber planes that attacked the airport in Benghazi, according to residents who witnessed the rare success in the struggle against Qaddafi's superior air power.
The rebels used three of their own seized planes and some helicopters to attack government troops fighting to advance on the city of Benghazi, said Mustafa Gheriani, a spokesman in the rebel base.
Charred vehicles, bullet-riddled pickup trucks and an overturned tank littered the desert highway where pro-Qaddafi forces had fought up to the entrance of Ajdabiya, a city of 140,000. An Associated Press Television News cameraman counted at least three bodies by the side of the road, evidence of fierce battles. Government troops were bringing in a stream of truckloads of ammunition, rockets and supplies.
A resident told the AP that Ajdabiya had been hit by hours of airstrikes but it was not clear if the government or rebels, who say they have at least three planes, are carrying them out.
"Qaddafi troops have not invaded the city on foot until now," said Moataz al-Ghariani, who lives in downtown Ajdabiya and is in touch with the rebels. "They are only imposing a siege from three fronts: the western, the southern and the eastern. No one can leave and no one can enter."
He said the rebels were surrounding a unit of Qaddafi forces at the eastern gates of the city.
A rebel spokesman told The Associated Press that Benghazi, 100 miles to the north along the Mediterranean coast, was "armed to the teeth" and the opposition is ready to defend it.
Libyan state television says pro-Qaddafi forces now control the western city of Misrata, but rebels and residents in the city deny the report, according to Reuters. Libya's state TV also reports that gunfire and explosions can be heard at the airport near Benghazi.
Libya's opposition battled to keep Qaddafi's forces at the gateway to rebel-held territory, hoping for help from the U.N. Security Council before his tanks and troops break through the city of Ajdabiya.
A Benghazi resident who did not want to be identified for fear of reprisals said the city's young men were volunteering to undergo basic military training. Those already trained were seeking more preparation to be battle ready.
More checkpoints were popping up at intersections and on main roads, manned by men in uniform armed with Ak-47s and backed by anti-aircraft guns mounted on pickup trucks.
Rebel spokesman Mustafa Gheriani said that the government tried to hit Benghazi's airport with an airstrike but missed.
The Red Cross said it was leaving Benghazi because of deteriorating security and moving to the city of Tobruk, further east.
Gheriani said by telephone from Benghazi that the opposition was hoping for a positive U.N. Security Council vote but "if not, we'll rely on ourselves and do what we can."
The U.S. wants the Security Council to approve planes, troops or ships to stop attacks by Gadhafi on the rebels, according to a diplomat familiar with closed-door negotiations Wednesday.
The Obama administration said it would not act without Security Council authorization, did not want to put U.S. ground troops into Libya, and insists on broad international participation, especially by Arab states, the diplomat said.
The Associated Press contributed to this report.