TRIPOLI (Reuters) - Libya's new government said it had tightened its grip on oasis towns which sided with Muammar Gaddafi, but faced a tough fight to take two remaining strongholds loyal to the ousted leader and bolster its credibility.
Forces of the National Transitional Council (NTC) said they controlled a string of desert towns in Libya's deep south, although they said Gaddafi loyalists were still holding out in pockets of at least one oasis.
So far they have failed to take the two much larger loyalist strongholds far to the north, Bani Walid and Gaddafi's hometown of Sirte, in a series of chaotic offensives which have raised questions about the NTC's ability to control the country.
Until Thursday, some parts of Sabha, the traditional base for Gaddafi's own tribe about 800 km (500 miles) south of Tripoli, had been occupied by fighters loyal to the leader who lost control of the capital and most of the country last month.
"Our revolutionaries are controlling 100 percent of Sabha city, although there are some pockets of resistance by snipers," NTC military spokesman Ahmed Bani said in Tripoli.
"This resistance is hopeless ... They know very well that at the end of the day they will show the white flag or they will die. They are fighting for themselves, not for the tyrant," he told reporters, referring to Gaddafi.
The U.N. atomic agency said on Thursday that Gaddafi's government had stored raw uranium near Sabha, after CNN reported that NTC forces had found a military site containing what appeared to be radioactive material.
In Vienna, International Atomic Energy Agency (IAEA) spokeswoman Gill Tudor said: "We can confirm that there is yellow cake stored in drums at a site near Sabha ... which Libya previously declared to the IAEA."
The NTC says it also controls Jufra, to the northeast of Sabha, and the nearby oasis towns of Sokna, Waddan, and Houn.
A manhunt for Gaddafi, who has been in hiding for weeks although he occasionally issues defiant audio messages, was drawing closer to its target, said Bani.
"We are doing our best looking for the tyrant. There is some news here and there that he ran away from Sabha to another place but it cannot be confirmed," he said.
The NTC, Libya's de facto government since Gaddafi's fall, has been anxious to show that it can establish firm control over a country riven by tribal and regional rivalries.
But, despite support from NATO warplanes, government forces have struggled to capture Sirte, the biggest city outside its control.
This is a complex job because many residents sympathize with Gaddafi. The city typifies the problem the NTC faces in reconciling the significant parts of the country that have tribal loyalties to Gaddafi or did not support the revolution.
A spokesman for Gaddafi, Moussa Ibrahim, said on Thursday that NATO air strikes and interim government forces' shelling of Sirte were killing civilians.
"Between yesterday and this morning, 151 civilians were killed inside their homes as the Grad rockets and other explosives fell upon their heads," he told Reuters by satellite phone from an undisclosed location.
His claims could not be verified as journalists are unable to reach the city. NATO comment was not immediately available.
Rebel fighters near Sirte and residents fleeing the city said pro-Gaddafi forces had been executing people suspected of sympathizing with the NTC.
North of Bani Walid, NTC military forces brought forward tanks and Grad rocket launchers for a renewed attempt to take the town although it was not clear when the attack might begin.
The offensive there has been frustrated by stiff resistance from well-drilled loyalist fighters, and also by a lack of organization among the NTC forces. They operate in disparate units based on their home towns, with little overall command.
Many fighters go into battle wearing flip-flop sandals, T-shirts and jeans and have no military training. "We don't take orders from the NTC. We listen only to our own commander," said Ziyad Al Khemri, a fighter from Zawiyah, just west of Tripoli.
If the NTC cannot swiftly take control of the country and its own forces, this may embarrass Western leaders, especially France's Nicolas Sarkozy and Britain's David Cameron, who took a gamble by backing the anti-Gaddafi leadership.
"We have set up a unified operations room to unite all brigades," said brigade commander Omar Kabout. "The purpose is to increase coordination and end all this chaos because many rebels have arrived without commanders. We need to put them into brigades and stop all this random shooting."
(Reporting by Tarek Amara in Tunis, Emma Farge in Tripoli, Maria Golovnian north of Bani Walid, Sherine El Madany east of Sirte, Alexander Dziadosz west of Sirte and Hamid Ould Ahmed in Algiers and Dina Zayed in Cairo; Writing by David Stamp; Editing by Andrew Heavens)