SABHA, Libya — Their fatigues don’t match and their pickup has no windshield. Their antiaircraft gun, clogged with grit, is perched between a refugee camp and ripped market tents scattered over an ancient caravan route. But the tribesmen keep their rifles cocked and eyes fixed on a terrain of scouring light where the oasis succumbs to desert.

“If we leave this outpost the Islamist militants will come and use Libya as a base. We can’t let that happen,” said Zakaria Ali Krayem, the oldest among the Tabu warriors. “But the government hasn’t paid us in 14 months. They won’t even give us money to buy needles to mend our uniforms.”

Krayem is battling smugglers, illegal migrants bound for Europe and armed extremists who stream across a swath of the Sahara near the porous intersection of southern Libya, Chad, Niger and Algeria. Since the 2011 Arab uprisings that swept away Moammar Kadafi and other autocrats, Western countries and Libya’s neighbors fear that this nation may emerge as an Islamist militant foothold.

Kadafi was replaced by a weak central government that has struggled with economic turmoil and the lack of judicial reform and a new constitution. The long-neglected south has grown more lawless. The Al Qaeda-linked militants, including Libyans, behind the January assault on a natural gas processing complex in Algeria that killed at least 37 foreigners traveled from Mali through Niger and Libya’s poorly patrolled hinterlands.

While the Libyan national army is rebuilding, the country is relying in part on ill-trained tribal militias rife with grievances, feuds and agendas. This volatile mix holds sway in the country’s southwest and in the northeast, where last year militants killed four Americans, including Ambassador J. Christopher Stevens, and trafficked guns and missiles to extremists in Egypt’s Sinai Peninsula and the Gaza Strip.

“Our concern is the Mali situation coming here,” said Fathallah Ali, assistant to the president of the local council in Sabha. “Much of the sophisticated and heavy weaponry looted from Kadafi’s military went to Islamic militants there and other parts of Africa. Al Qaeda is moving in this direction.”

Even under Kadafi, the nation produced Islamic militants who reached well beyond the country’s borders. Libyan extremists are now connected to an Al Qaeda branch in Algeria, rebels in Syria and the fighters trying to establish an Islamic caliphate in Mali. Security officials also are concerned about reports of militant training camps with caches of weapons hidden in the desert south of Sabha.

Government officials in the south shy away from discussing the region’s chaos. An activist was recently shot and killed after publicly criticizing the lack of law and order. Much of the danger stems from tribal animosities that were suppressed during four decades of Kadafi’s rule and are now playing out in the kind of security vacuum that Islamic militants have exploited in countries such as Somalia and Yemen.

The Tabu, who are Africans, have been battling the rival Arab Awlad Sulayman clan for more than a year. At least 130 people have died. Peace talks have been complicated by joblessness, rising drug and alcohol abuse and skirmishes over smuggling networks stretching from the borders of Algeria and Chad.

The streets of Sabha, the main city in the south, rattle with gunfire and the gripes of desperate men waiting for work, sitting on dusty curbs with buckets, paint rollers and chisels. Jailbreaks are common. Libyan news reports said in January that three bodyguards were wounded when gunmen fired on a hotel housing Mohammed Magarief, president of the national congress.

In the city’s hospital, doctors are pistol-whipped and patients shot in their rooms by rival tribesmen. The sick slump in hallways. There is no CT scan or MRI machinery; a trauma victim is likely to die before he can be driven 400 miles north to a better hospital in Tripoli.

“We’re treating illnesses we’ve never seen before in languages we don’t understand,” said Dr. Othman Habib, a pediatrician. “More and more migrants are coming from Chad and Mali. Libya’s borders are open and poorly guarded. We never saw malaria before, but now we see it all the time. We’re overwhelmed. The hospital is full of germs and bacteria. Rats. This is shameful, but it’s true.”

A bereft father, his tunic wet with the blood of a son hit by a car, walked past.

“One man was brought in with a gunshot wound not long ago,” said Habib. “We fixed him and put him in intensive care. But his enemies came to the hospital that night and shot him 18 times. We operated and he lived. We hid him in the women’s ward and then sneaked him out of town.”

Dr. Yusef Farag, a surgeon, listened and said, “We have 200 beds. We’ve turned 500 people away. This hospital serves the whole south, but we can admit no more. We have no neurosurgeon. We have no oncology doctor. There are too many weapons and too many comas. It’s a disaster.”

Despair permeates the dirt alleys not far from the hospital that curl through the cinder block slums of Tabu tribesmen.

“Clashes between border tribes have increased,” said Adam Ahmed Dazi, a Tabu councilman who sat at a desk stamping papers while complaining about the lack of financial support from Libya’s central government. “Tribal militias and smugglers have better arms. But smuggling is in the hands of rich people with trucks. The Tabu in this neighborhood barely have bicycles. But we are like a towel. Everyone wipes the bad on us.”

He sighed, his narrow frame almost lost in his coat.

“When you look at the revolution,” he said, “not much has changed in the southern tribal areas. It hasn’t gotten better, except that we are now free to practice our traditions without fear anymore of the racist Kadafi regime.”

The road out of Sabha cuts through a green blush of oasis and a series of checkpoints — the first controlled by a militia, the second by the national army — in a strange hodgepodge of overlapping interests. Krayem and his Tabu tribesmen, their faces covered with scarves and sunglasses, guard a third checkpoint near rock formations at the edge of blowing sands.

“The desert is wide with many roads,” said Krayem, a man seemingly wearing away bit by bit. His teeth are loose, a nostril is gouged and he is missing a finger that was shot off by soldiers exacting retribution for his defection from Kadafi’s army during the revolution.

“Anything forbidden they try to smuggle through here,” he said. “The military can’t control this territory on its own. If we left this checkpoint even for 30 minutes bad people would come. The government doesn’t pay us. We do this to protect our country.”

He tugged the brim of his camouflage hat.

“But men need to feed their kids,” he said. “That’s why many are moving into the smuggling trade.”

They traffic in rocket-propelled grenades, stolen cars, hashish and government-subsidized gasoline and flour. Krayem has seen it all.

He stepped toward the broken road as dusk fell across market tents, thicket and scrub. The wind cooled. A big truck, draped with boys and barrels and lumbering like a collapsing house on wheels, approached. His men checked their guns and prepared for night.

“The next checkpoint is 150 kilometers away,” he said, nodding to the outskirts of Sabha and the encroaching desert. “We don’t have enough patrols to cover all what’s in between.”

jeffrey.fleishman@latimes.com