Benghazi: General Abdel Fatah Younes, commander of forces fighting to oust Libyan leader Muammar Gaddafi, has been killed in mysterious circumstances, dealing military and political blows to the rebels.

Younes was shot dead by an armed gang after he was summoned from the front by the rebel National Transitional Council "for questioning over military issues," NTC chairman Mustafa Abdel Jalil said late on Thursday.

His killing, and that of two military officers, is seen as a sign of divisions within the ranks of the rebels in eastern Libya even as they make fresh advances in the west in a pre-Ramadan push to drive Gaddafi out.

"With all sadness, I inform you of the passing of Abdel Fatah Younes, the commander-in-chief of our rebel forces," Abdel Jalil said in a carefully worded statement at a press conference in Benghazi, the rebels' eastern capital.

"The person who carried out the assassination was captured," a somber looking Abdel Jalil said without elaborating. He added there would be three days of mourning in Younes's honour although his body has yet to be recovered.

Rumours circulated in Benghazi that Younes, Libya's former interior minister and number two in Gaddafi's regime prior to his defection in February, was arrested and killed by the rebels themselves after it was alleged his family still had ties with Gaddafi.

The scenario that the rebels have started fighting among themselves could pose awkward problems for the many Western powers who have recognised the NTC as the sole legitimate authority in Libya.

Rebel leaders tried to dampen down the speculation. "I ask you to refrain from paying attention to the rumours that Gaddafi's forces are trying to spread within our ranks," Abdel Jalil told journalists after a lengthy closed door meeting with NTC members.

Moments after the announcement, two vehicles loaded with an anti-aircraft gun and at least a dozen armed men shooting in the air arrived at Tibesti hotel, where the announcement was made.

A witness said that they later managed to enter the hotel with their weapons but security forces calmed them down and convinced them to leave.

"They shouted 'You killed (Younes)'," in reference to the NTC, he added.

At least three loud explosions shook the centre of Tripoli late Thursday, as Libyan television reported that planes were flying over the Libyan capital, which has been the target of NATO air raids.

Al-Jamahiriya television reported that several "civilian sites" had been bombed by NATO on Thursday.

Libyan rebels seized two localities near the Tunisian border earlier in the day as part of their offensive ahead of the start early next week of the Muslim fasting month of Ramadan, an AFP correspondent said.

The first was the town of Al-Ghazaya, some 12 kilometres from the frontier and the second was Umm Al-Far, a hamlet of a few hundred inhabitants 10 kilometres northeast of there.