WRAPUP 6-Libya rulers say they seize Gaddafi desert outposts
(Adds Jufra's capture, chemical weapons find, Arrai TV report)
* Chemical weapons depot uncovered - NTC spokesman
* Bani Walid and Sirte still resisting
* NATO extends mission for three months
* Interim PM says new cabinet within 10 days
TRIPOLI/NORTH OF BANI WALID, Libya, Sept 21 (Reuters) - Libya's interim rulers said on Wednesday they had captured one of Muammar Gaddafi's last strongholds deep in the Sahara desert, finding chemical weapons, and largely taken control of another.
With the National Transitional Council (NTC) struggling to assert full control over the country, military spokesmen said its forces had seized the outpost of Jufra about 700 km (435 miles) southeast of Tripoli, and most of Sabha.
"The whole of the Jufra area -- we have been told it has been liberated," spokesman Fathi Bashaagha told reporters in the city of Misrata. "There was a depot of chemical weapons and now it is under the control of our fighters."
His comments could not be confirmed independently. Under Gaddafi, Libya was supposed to have destroyed its stockpile of chemical weapons in early 2004 as part of a rapprochement with the West under which it also abandoned a nuclear programme.
However, the Organisation for the Prohibition of Chemical Weapons says Libya kept 9.5 tonnes of mustard gas at a secret desert location, although it could no longer deliver it.
Gaddafi loyalists have been holding out in Jufra and Sabha along with the bigger strongholds of Bani Walid, southeast of Tripoli, and Gaddafi's hometown of Sirte since the fall of the capital in August.
"We control most of Sabha apart from the al-Manshiya district. This is still resisting, but it will fall," said another NTC military spokesman, Ahmed Bani.
CNN, citing a correspondent in Sabha, reported that NTC fighters had occupied its centre on Wednesday after taking the airport and a fort the day before.
NATO countries gave the NTC another boost by extending for three more months the air cover that helped anti-Gaddafi fighters to victory.
However, chaos prevailed among fighters besieging Gaddafi's other two remaining major strongholds. Several attempts by NTC fighters to take Bani Walid and Sirte in the past week have ended in disarray and panicked retreat.
At Bani Walid, bored militiamen fired weapons at camels and sheep while awaiting orders on Wednesday, as much a danger to themselves as to Gaddafi fighters holed up in the town.
One man shot his own head off and killed another fighter while handling a rocket-propelled grenade in full view of a Reuters team. In another incident, a fighter wounded himself and another fighter after losing control of his machinegun.
Seven NTC fighters were also killed in an ambush by pro-Gaddafi soldiers inside Bani Walid, NTC officials said.
At Bani Walid, troops from other areas have been arguing with local fighters, and there has been talk of traitors infiltrating the ranks and sabotaging the assault.
NTC official Abdullah Kenshil told Reuters that pro-Gaddafi forces in Bani Walid had killed at least 16 civilians there in the last two days after suspecting they supported the NTC.
"They were killed in cold blood. They were all civilians and they were killed execution-style," he said. His account could not be independently verified.
Sporadic fighting also continued outside Sirte, where an NTC push from the east toward Gaddafi's birthplace has been blocked for days by heavy artillery fire from loyalist soldiers.
Fighters making their way back from the front line said they were meeting fierce resistance at Khamseen, 50 km (30 miles) east of Sirte, and that they lacked the firepower to respond.
"I'm 100 percent sure that there is someone important in Sirte, either Gaddafi himself or one of his sons, because his forces have become suicidal in the Khamseen area," NTC fighter Hamed al-Hachy told Reuters.
Efforts to take control of all of Libya's territory are taking place alongside attempts to reshuffle the interim government. A plan to do so this week collapsed after members of the current council failed to agree.
The NTC has its roots in the eastern city of Benghazi, but most of the fighters who captured Tripoli came from the west, and Interim Prime Minister Mahmoud Jibril is under pressure to reflect this better in his cabinet.
Jibril said in New York, where he is attending the U.N. General Assembly, that he expected to name a new government within 10 days.
Among issues being debated were the number of ministries in the new government and whether they would be in Tripoli or divided between eastern and western Libya, he added.
U.S. President Barack Obama called on Gaddafi's loyalists to give up and said the U.S. ambassador would return to Tripoli.
"Those still holding out must understand -- the old regime is over, and it is time to lay down your arms and join the new Libya," he said.
NATO, which took command of a military mission on March 31 under a U.N. mandate to protect Libyan civilians, agreed at a meeting of ambassadors of its 28 member states in Brussels to extend the mission for three more months, a NATO diplomat said.
Britain said its planes had struck at pro-Gaddafi troops in three areas and destroyed bases in Sirte and Bani Walid.
The Syrian-based Arrai TV, which has broadcast several audio messages from Gaddafi, his sons and his aides, said NATO warships and planes had hit a hospital in Sirte on Wednesday, wounding a Ukrainian doctor and patients.
It was not immediately possible to verify the report. Previous allegations of NATO causing civilian deaths have rarely been backed up with evidence.
Tunisia said its troops had killed several infiltrators on Wednesday in clashes near the border with Algeria.
Helicopters destroyed seven vehicles mounted with anti-aircraft guns, which had been used to fire at a Tunisian army helicopter, a Defence Ministry spokesman said.
Armed Libyans clashed with Tunisian troops last month in the final days before the fall of Tripoli. (Reporting by Joseph Logan and Emma Farge in Tripoli, Maria Golovnina north of Bani Walid, Alexander Dziadosz west of Sirte, Sherine El Madany east of Sirte, David Brunnstrom in Brussels, Barry Malone in Tunis, John Irish, Matt Spetalnick and Laura MacInnis at the United Nations and Stephen Addison in London; Writing by Barry Malone and Joseph Nasr; Editing by David Stamp)