NATO planes bombed the Tripoli compound of Libyan leader Moamer Gaddafi for the second time on Tuesday, a witness said, DPA reported.
There was fire in the Bab al-Aziziya compound and heavy black smoke was seen coming out, he added.
The whereabouts of Gaddafi, who turns 69 on Tuesday, are not known. His son Saif al-Arab was killed in a NATO airstrike on the compound on April 30.
Four explosions were heard earlier in the day in the Libyan capital, three of them in Bab al-Aziziya.
Witnesses said that attacks were also targeting intelligence offices in central Tripoli.
The airstrikes began at the end of March under a United Nations Security Council resolution reinforcing a no-fly zone to ensure the safety of civilians in the conflict between Gaddafi's forces and rebels.
Protests against Gaddafi, who has been in power for 42 years, began in mid-February, but soon turned into an armed conflict following a lethal government crackdown on demonstrators.
The attack comes after Mikhail Margelov, Russia's special envoy on Africa, arrived in the rebel-stronghold of Benghazi for talks with the opposition.
He is scheduled to meet with members of the Interim Transitional National Council (ITNC).
The visit is seen as a further isolation of the embattled Gaddafi and his regime, as it comes following a similar visit by a Chinese envoy. The Chinese ambassador to Qatar recently met the chairman of the ITNC, Mustafa Abdul-Jalil.
Both China and Russia have maintained good relations with Gaddafi since he took power in a 1969 coup.
The pair of veto-holding permanent members of the UN Security Council were both opposed to NATO's airstrikes on military installations controlled by Gaddafi.