Libyan rebels made gains in the oil port of Brega on Thursday after days of inconclusive fighting for control key northeastern cities, opposition sources said, DPA reported.
For days, the opposition has been trying to regain lost ground in the east after Moamer Gaddafi's force reclaimed several key coastal cities, forcing the rebels back eastwards to the city of Ajdabiya.
But Gaddafi's opponents were able to push towards Brega overnight, despite lashing out at NATO for not moving quickly enough to stop Gaddafi's attacks.
NATO has rejected the criticism, saying the pace of its operations continues unabated.
Despite weeks of coalition airstrikes on Gaddafi's forces, his military capabilities remain quite substantial, according to a Pentagon official quoted in the New York Times on Thursday.
French Foreign Minister Alain Juppe said Thursday that the next meeting of a contact group set up to guide the international intervention in Libya will meet in Qatar on April 13.
Meanwhile, the state-news agency JANA reported that Gaddafi sent a letter to US President Barack Obama on Wednesday, but the contents of the letter were not made public.
Gaddafi reportedly asked Obama to intervene to halt the NATO military campaign, broadcaster CNN reported. Gaddafi called the NATO operation an "unjust war against a small people of a developing country" and said the opposition rebels were terrorists and members of al-Qaeda, CNN said, citing an unnamed US official familiar with the letter.
The embattled leader has recently used his artillery to shell oil fields controlled by the rebels in the east.
However, the targeted attacks did not deter the opposition from exporting oil earlier this week.
According to a spokesman for the rebels, an oil tanker left the eastern port city Tobruk, carrying crude from rebel-controlled oil fields.
Meanwhile, Gaddafi suffered another diplomatic blow when his former energy minister, Omar Fathi Bin Shatwan, defected to Malta.
Shatwan arrived in Malta a week ago on board a boat from the besieged city of Misurata, a spokesman for the Maltese Foreign Ministry who spoke told the German Press Agency dpa.