|The defection of Shokri Ghanem would be a huge loss to Gaddafi's government [Reuters]
Libya's oil minister has reportedly defected and fled to Tunisia.
Shokri Ghanem, who also chaired the National Oil Corporation, is said to be on his way to the capital, Tunis.
Hoda Abdel-Hamid, one of Al Jazeera's correspondents in Libya, said a border guard confirmed the defection.
"He told us the minister had crossed into Tunisia two days ago and that he was alone, not with his family," she said.
"He mentioned he had tried to cross before but was held in Libya. We cannot confirm this."
Rebels fighting to end the 41-year-old rule of Muammar Gaddafi, Libya's embattled leader, also said they had information that Ghanem, 68, had defected.
However, rebels and Arab media reported on a previous occasion that Ghanem had stepped down, but he later re-appeared and said he was in his office and working as usual.
If confirmed, Ghanem would be the latest high profile Libyan official to leave the Gaddafi government. In March, Gaddafi's foreign minister, Moussa Koussa, defected.
Ghanem has been in charge of the oil ministry since 2006 and was previously prime minister. His oil ministry is the biggest income generater for the country.
Libya has Africa's largest oil reserves, at 41.5 billion barrels.
Rebels have taken Benghazi and the oil-producing east of the North African country, their uprising helped by a NATO bombing campaign sanctioned by the UN to protect civilians.
Meanwhile, Russia hosted a representative of Gaddafi's government in its capital, Moscow, on Tuesday when it called on the Libyan government to stop using force against civilians, comply fully with UN Security Council resolutions and withdraw armed groups from cities.
"The answer we heard cannot be called negative," said Sergei Lavrov, the Russian foreign minister.
He said that Libya was ready to look at peace proposals based on those suggested by the African Union and to comply with Security Council resolutions.
"The only things that our interlocutors from Tripoli noted today was the necessity of the insurgents accepting analogous steps and that NATO also stopped bombing," Lavrov said, adding that it remained to agree terms and a timeframe for a truce.
The talks indicate Russia's desire to act as peace maker and preserve its influence in Libya, where it has billions of dollars of arms, energy and infrastructure deals.
Russia is one of five permanent Security Council members. It abstained from voting on the resolution authorising military intervention in Libya and has accused NATO of going beyond the bounds of the resolution in its bombing.
In the capital, Tripoli, NATO air planes reportedly hit two buildings on Tuesday, including one which a Libyan spokesman said contained files detailing corruption cases against government officials who had defected to the rebels.
Officials summoned reporters after the attack in the early hours to visit the two damaged buildings which they said housed internal security forces and Libya's anti-corruption agency. One building was in flames.
"We believe that NATO has been misled to destroy files on their corruption cases," said spokesman Mussa Ibrahim.
Ambulances were at the scene of the buildings on either side of a street although there was no sign of any casualties.
Meanwhile, on the frontline, Libyan rebels have virtually abandoned the Dehiba-Wazzin border post on the frontier with southern Tunisia.
At least three rebels were killed and many injured by Libyan government shell fire, a witness called Walid said on Tuesday.
Abdel-Hamid said that grad rockets had landed on Tunisian territory.
"About four have fallen inside Tunisia inside the [Dehiba-Wazzin] border," she said.
"That border is key in the fight because it is a lifeline for rebels. Since they took control of it, Gaddafi's forces have been doing everything they can to regain control of that border."
A Reuters photographer at the border post said: "There are lots of injured crossing over in ambulances from the Libyan side. We were told that some people were killed as well."
Meanwhile, seven people were killed on Tuesday in Misurata during clashes between rebels and forces loyal to Gaddafi, a doctor at a hospital in the rebel-held Libyan city said.
The doctor said most of the casualties were rebel fighters killed in battles on the western and eastern edges of the city.