Muammar Qaddafi's troops seized the strategic Libyan oil town of Brega on Sunday, forcing rebels to retreat eastward and putting extra pressure on world powers still deliberating on a no-fly zone.
The government offensive had already driven the rebels out of Ras Lanuf, another oil terminal 100 km to the west on the coast road, and the seizure of Brega and its refinery deprived the rebels of more territory and yet another source of fuel.
The government, in a message on state television, said it was certain of victory and threatened to "bury" the rebels, who it linked to al Qaeda and "foreign security services."
A United Nations humanitarian co-ordinator sent to Tripoli told Reuters he wanted access to areas on both sides of the conflict to assess the impact of the violence on civilians.
On the diplomatic front, France said it would intensify its efforts to persuade world powers to impose a no-fly zone on Libya, where Qaddafi's troops seemed to have gained the initiative in their struggle with rebels seeking an end to his four-decade rule.
Meanwhile Libya said it would welcome an African Union panel that will try to help resolve the crisis, but condemned an Arab League call for a no-fly zone over the country.
"Brega has been cleansed of armed gangs," a Libyan government army source told state television.
Defeated rebel fighters were demoralised
Brega is 220 km (135 miles) south of the rebel stronghold of Benghazi and Ajdabiyah is the only sizeable town between the two. From Ajdabiyah there are separate roads to Benghazi and to Tobruk, close to the border with Egypt.
The flat desert terrain means the government's air supremacy and tanks outweigh the rebels' enthusiasm and light weaponry. Only towns and cities provide some cover for the insurgents and, to some extent, lessen the odds against them.
State television carried a confident message from the authorities. "We are certain of our victory, whatever the price," it said.
"Those acts of division will be buried together with those who committed them, who are linked to foreign security services and the terrorist organisation al Qaeda," it said.
Rashid Khalikov, the UN humanitarian co-ordinator for Libya, said in an interview he wanted unimpeded access: The speed of the government advance may overtake drawn-out diplomatic wrangling on whether or how to impose a no-fly zone.
The United States said the Arab League's call for a UN no-fly zone to protect Libyan cities was an "important step", but Washington remained cautious about military intervention.