The chairman of Libya's National Oil Corporation has defected from Muammar Gaddafi's administration and fled to neighbouring Tunisia, a Tunisian security source said.
Libyan rebels also said they had information that Shokri Ghanem, 68, had defected, a move that if confirmed would deal a major blow to Gaddafi's efforts to shore up his 41-year rule.
'He is in a hotel with a group of other Libyan officials,' the Tunisian source told Reuters, saying Mr Ghanem had been staying in the south of the country.
Another Tunisian security source said he was on his way to the capital Tunis.
However, a government official in Tripoli said there was no sign Mr Ghanem had defected.
Three months into the unrest, rebels hold Benghazi and the oil-producing east of Libya, helped by a NATO bombing campaign sanctioned at the UN to protect civilians.
But the military victory rebels once sought seems a distant prospect and many pin their hopes on a collapse of central power in Tripoli driven by disaffection and defections.
Mr Ghanem, an internationally respected technocrat, is credited with liberalising Libya's economy and energy sector.
Rebel finance and oil minister Ali Tarhouni told Reuters on a visit to Doha that he understood Mr Ghanem had left his post, and said he hoped to represent Libya at an OPEC meeting in June.
Libya is estimated to have lost two thirds of its oil output since the unrest began.
Rebels and Arab media reported on a previous occasion that US-educated Mr Ghanem had stepped down, but he appeared later and said he was in his office and working as usual.
The most prominent Libyan defector so far is Moussa Koussa, the former foreign minister, who fled to Britain earlier this year.
Meanwhile, Libyan state television said Libyan forces had hit a NATO warship that was shelling areas of the rebel-held city of Misrata, but NATO denied the report, saying it was 'totally fabricated'.
A doctor in the western city said at least seven people were killed during fighting between rebels and government forces earlier today. Most of the dead are believed to be rebels.
British aircraft and navy ships attacked a training base for bodyguards for Gaddafi's inner circle and intelligence buildings in the capital, the British Defence Ministry said.
