Suspicion for the recent murder of the opposition forces commander Abdel Fattah Younes has fallen on a rebel group of fighters from the town of Derna in Eastern Libya. Gadaffi's government has described it as a "hotbed of religious fundamentalism", which the town's residents refute.

Saif al-Islam, Muammar Gaddafi's son, in an interview witn the New York Times, said he was forging an alliance with Islamist rebels against their liberal allies, in what appears to be a bid to divide the Libyan opposition groups. 

The newspaper quoted a Ali Sallabi, a senior Islamist rebel leader who confirmed he had been in contact with Gaddafi's son. However, he denied forging an alliance with the ruling family, pledged his continued support for the opposition and denied a split with the liberal wing of the six-month-old rebellion.

"Saif al-Islam's statement is baseless. It's a lie that seeks to create a crack in the national accord," Sallabi said.  Sallabi acknowledged making conversations with Saif.

"Our dialogue with them is always based on three points: Gaddafi and his sons must leave Libya, the capital (Tripoli) must be protected from destruction and the blood of Libyans must be spared. There is no doubt about these constants," he said.

"We support pluralism and justice. Libyans have the right to build a democratic state and political parties." Sallabi said relations between the Islamists and seculars are "strong."

Meanwhile, The rebels scored a victory on Thursday, bringing a ship with a seized cargo of government-owned fuel into their port. The docking in Benghazi of the Cartagena, a tanker carrying at least 30,000 tonnes of gasoline, boosts an insurgency which has won broad international military and diplomatic backing but is struggling to oust Gaddafi.

Gaddafi has so far remained in control of the capital Tripoli despite severe fuel shortages and rebel advances on three fronts, backed since March by Western air strikes. He has defied hopes in Western states of a swift exit, forcing them to await progress on political and military fronts.

Al Jazeera's Tony Birtley reports from Derna.