Loud explosions were heard in the Libyan capital Tripoli Wednesday morning, with residents saying NATO warplanes struck at government sites, according to the opposition, DPA reported.
The opposition Libya TV, which began broadcasting out of Qatar end of March, reported that it was "the heaviest bombing of the Libyan capital in weeks".
Since mid-February, Libyan activists have armed themselves in a battle to oust Moamer Gaddafi from power, after 42 years at the helm. The opposition claims that more than 12,000 people have been killed in the fighting.
The unconfirmed reports of explosions in Tripoli were heard for almost an hour, according to online activists.
NATO planes were also said to have hit at least four sites in Tripoli overnight.
One strike hit a building that locals said was used by a military intelligence agency while another targeted a government building that officials said was sometimes used by parliament members, reported Libya TV.
This came after NATO said Tuesday it began a second phase of its military operation, this time targeting Gaddafi's command centres.
Although much of the capital remains under Gaddafi's control, rebels have been more openly operating out of the western part of Tripoli in recent days, with the Free Libya flag spotted on several schools and bridges.
Rebels have also claimed gains in the besieged coastal city of Misurata, 200 kilometres east of Tripoli.
Residents told Libya TV that fighting was taking place both on the outskirts of Misurata and the near the city's airport, where Gaddafi's forces fight to hold ground.
The opposition hopes that by pushing Gaddafi's forces fully out of Misurata they can advance westward on to Zlitan and Tripoli.
Meanwhile, rebels retreated shortly after they said they had advanced late Tuesday 40 kilometres outside of the eastern town of Ajdabiya amid reports that NATO was launching strikes in the area against Gaddafi's forces.
The rebels have been trying for weeks to advance west of Adjabiya, but have been unable to regain control of the road linking the town to the oil-port city of Brega, which is under Gaddafi's control.
The European Union chief Catherine Ashton said Wednesday the body plans to open an office in the eastern rebel stronghold of Benghazi to support Libya's population and the rebels' Interim Transitional National Council.