The military alliance said Operation Unification Protector includes an arms embargo, a no-fly zone and "actions to protect civilians and civilian centers," CNN reported.
The NATO takeover came after a U.N. Security Council resolution allowing member states "to take all necessary measures" short of occupation to protect civilians under the threat of attack by Libya strongman Moammar Gadhafi.
After recording successes in taking over several town and oil centers, opposition forces met resistance in Sirte and have been driven back by pro-Gadhafi forces, losing much of the gains they had made.
Opposition troops, seeking Gadhafi's ouster after four decades of rule, lack weaponry, training and organization to fight Gadhafi's military troops and their sustained assaults. To help level the field, rebels have asked the international community for better, more powerful weapons.
Saddoun el-Misurati, a spokesman for the Libyan opposition in Misurata, told CNN rebels were relying on the coalition for help.
"Our greatest hope will rely mainly on the support of the international coalition forces in the form of change of tactics from the air to target tanks and heavy artillery and also take out groups of sniper positions on buildings and in the city," he said.
Col. Ahmed Omar Bani, the rebels' military spokesman, said "countries across the world" have offered weapons, the British newspaper The Guardian reported. While revealing neither the countries nor the type of weapons, he did say rebels needed anti-tank weapons and radios.
Bani also admitted arms or ammunition haven't arrived as yet, the newspaper said.
Weather conditions barred a NATO-led coalition from launching more airstrikes to try to weaken Gadhafi's ability to attack civilians, a U.S. representative said Wednesday.
While U.S. and British officials said nothing's been decided about whether to provide arms to the opposition, a U.S. intelligence source told CNN the CIA is in the country to increase the "military and political understanding" of the situation.
Earlier, officials told The New York Times U.S. and British operatives weren't in close contact with the rebels, but targeting information provided to NATO air forces could reduce the effectiveness of Gadhafi's military and speed up departure from power.