MISRATA, Libya (Reuters) - Islamic State militants have shifted to desert valleys and inland hills southeast of Tripoli as they seek to exploit Libya's political divisions after defeat in their former stronghold of Sirte, security officials say.
The militants, believed to number several hundred and described as "remnants" of Islamic State's Libya operation, are trying to foment chaos by cutting power and water supplies and to identify receptive local communities, the officials said.
They are being monitored through aerial surveillance and on-the-ground intelligence, but Libyan officials said they cannot easily be targeted without advanced air power of the kind used by the United States on Jan. 19, when B-2 bombers killed more than 80 militants in a strike southwest of Sirte.
For more than a year, Islamic State exercised total control over Sirte, building its primary North African base in the coastal city. But it struggled to keep a footing elsewhere in Libya and by December was forced out of Sirte after a six-month campaign led by brigades from the western city of Misrata and backed by U.S. air strikes.
The jihadist group lost many of its fighters in the battle and now has no territory in Libya, but fugitive militants and sleeper cells are seen to pose a threat in a country that has been deeply fractured and largely lawless since the 2011 uprising that toppled Muammar Gaddafi.
The threat is focussed south of the coastal strip between Misrata and Tripoli, arcing to the southeast around the town of Bani Walid and into the desert south of Sirte, said Ismail Shukri, head of military intelligence in Misrata.
One group of 60-80 militants is operating around Girza, 170 km (105 miles) west of Sirte, another group of about 100 is based around Zalla and Mabrouk oil field, about 300 km southeast of Sirte, and there are reports of a third group present in Al-Uwaynat, close the Algerian border, he said.
Some fighters were based outside Sirte before last year's campaign, some fled during the battle and some have arrived from eastern Libya where they have been largely defeated by rival armed factions.
"They work and move around in small groups. They only use two or three vehicles at a time and they move at night to avoid detection," said Mohamed Gnaidy, an intelligence official with forces that conducted the campaign in Sirte.
Those forces published pictures in the wake of last month's U.S. strike showing hideouts dug into the sand, temporary shelters camouflaged with plastic sheeting and branches, stocks of weapons and satellite phones.
"This area is very difficult so it's hard for our forces to deal with them," said Shukri, pointing to satellite images of steep rocky banks and tracks in the sand southwest of Sirte. "The only solution to eliminate them in this area is through air strikes."
Mohamed Gnounou, a Misrata-based air force spokesman, said the militants had been monitored for 45 days ahead of the U.S. strike. "It confirmed a large number of individuals who were preparing something new in this place, as well as developing a strategy to head to new areas." The areas included rural districts near the coastal cities of Al Khoms and Zliten, between Misrata and Tripoli, and the region around the southern city of Sabha, he said.
Islamic State fighters had received logistical help from civilians and had paid some of them to help cut off power and water supplies, including by sabotaging a water link to Tripoli in the Great Man-made River system built by Gaddafi, and attacking electricity infrastructure near the southern city of Sabha, where there have been long blackouts in recent weeks, said Gnounou.
"Daesh (Islamic State) destroyed more than 150km of electricity pylons in the south between Jufra and Sabha. These acts fuel crisis and frustration in Libya, as well as giving an opportunity for gold diggers who smuggle through the open borders and make easy money from Daesh," he said.
Sirte suffered extensive damage during the battle against Islamic State. Military officials from Misrata say they have the city secured and some residents have begun to return to central neighbourhoods.
But they also complain about a lack of support from the U.N.-backed Government of National Accord (GNA) in Tripoli and are nervous about military advances by forces loyal to military commander Khalifa Haftar to the east and south of Sirte.
Haftar, who has rejected the GNA, was on the opposite side to Misrata's brigades in a conflict that flared up across Libya in 2014, just as Islamic State was gaining strength.
Both sides accuse the other of using Islamic State to their advantage, while waging separate campaigns against jihadists.
"The support we are getting is not equivalent to the risk we face or the sacrifice we have made," said Shukri. "We need the political authorities, the (GNA) to continue the next step."
Additional reporting by Ahmed Elumami; Editing by Janet Lawrence