Air strikes targeted a militia in Tripoli as rival armed groups from Misrata and Zintan battled for supremacy in Libya amid a worsening bout of violence.
Renegade General Khalifa Haftar's air force was responsible for Monday's air strikes, one of his commanders said.
None of the militias had been thought to own warplanes, while the central government has only an outdated air force.
However, Libyan television news channels speculated that the country's neighbours might be behind the overnight air strikes, which Tripoli official Mohammed al-Kriwi said had killed about five people and wounded as many as 30.
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The air attacks escalate a struggle between Islamist and more moderate forces as well as between militias from different cities all vying for power.
Forces from Zintan had allied themselves with Haftar and stormed parliament in May, saying it had an Islamist agenda.
Referring to Haftar's campaign against Islamists which he had launched in Benghazi, his air defence commander, Saqer al-Jouroushi, told Reuters on Monday: "We, the Operation Dignity, officially confirm to have conducted air strikes on some militias' locations belonging to Misrata militias."
Clashes between Haftar's forces and Islamist fighters also broke out in Benghazi around 5pm with one of his helicopters opening fire.
A Reuters reporter at the scene heard loud explosions. Eleven of Haftar's men were taken to hospital, a military source said.
Tripoli residents said they heard several jets overhead after midnight, followed by loud explosions. No more planes were heard but fighting resumed in parts of the city in the morning.
A Zintani source said fighters in his unit saw planes bombing a Misrata militia position. "Our forces at the airport saw massive and accurate bombings," he said. Reuters reporters were not immediately able to access the area.
The Tripoli government said it did not know to whom the warplanes belonged. "The government does currently not have any convincing indications to establish which side was behind this," it said in a statement.
An Egyptian security source said air traffic between the two countries had been interrupted for six hours and that Libyan air controllers had cited security reasons.
Some Tripoli residents, tired of daily fighting disrupting power and food supplies, hope NATO will intervene in Libya.
On Sunday, the UN Mission in Libya said it "deeply regrets that there was no response to the repeated international appeals and its own efforts for an immediate ceasefire".
The new UN special envoy, Bernardino Leon, who is due to start his job on September 1, said he might travel to Tripoli soon.