After a crackdown pushed them out of Nigeria's northern cities, Islamist militant group Boko Haram have regrouped, rearmed and are staging a bold comeback that has already allowed them to seize control over parts of the northeast.
Using porous borders with Chad, Niger and Cameroon in the desolate scrubland around Lake Chad, they are smuggling bigger weapons, staging cross-border raids, killing and kidnapping in an escalation of violence that could further draw Nigeria's neighbors into its counter-insurgency fight, security officials say.
The Islamists now control at least 10 of the 27 local council areas in Borno state, Nigeria's most remote northeastern region on the edge of the Sahara and a relic of one of Africa's oldest medieval Islamic empires, security sources there say.
One says the real figure could be closer to 20, as local councilors fearing assassination have fled, leaving a power vacuum filled by bearded radicals with automatic rifles.
Boko Haram's struggle for an Islamic state has killed thousands since 2009 and is the main threat to Africa's top oil producer, although its fighters have so far not struck anywhere near the southern oil fields.
When Borno's governor Kassim Shettima briefed visiting senators and military advisers in a confidential security meeting on May 7, he said something that stunned them: Boko Haram were on the verge of seizing control of his state.
"What the governor said was frightening. He informed us there is a possibility that this state will be taken over by Boko Haram ... that they have the ability to do whatever they wanted here," senator Abdul Ahmed Ningi, a delegate and deputy majority leader for the ruling party, said after the meeting.
"I had thought Boko Haram had been subdued to some extent."
Movement in flux
A wave of Islamic fervor took hold of northern Nigeria during an economic crisis in the early 1980s, triggering riots in the North’s main city of Kano and later prompting many states to introduce Sharia law from 1999.
In 2002, a cleric called Mohammed Yusuf founded a radical Islamist movement in Borno, later nicknamed 'Boko Haram' or 'Western education is sinful' in the northern Hausa language because of its opposition to Western cultural influences.
A military crackdown during an uprising in 2009 led to the deaths of 800 people, including Yusuf, who died in police custody.
Far from being silenced, they struck back, first shooting or throwing bombs at police off the back of motorcycles, then graduating to increasingly sophisticated bomb-making technology.
By late last year it seemed the militants had been chased out of city centers and were losing the ability to carry out large-scale attacks, but Boko Haram have repeatedly proved masters of recovering from apparent defeat.
A coordinated strike by some 200 Boko Haram fighters on an army barracks, police station and prison in the town of Bama last week that left 55 people dead and freed more than 100 prisoners was the latest evidence that they have recovered their strength.
Initially funded by northern politicians who later distanced themselves from the militants, Boko Haram have forged growing links with Saharan Islamists such as al Qaeda in the Islamic Maghreb, giving them new access to funding and training.
The road from Borno's capital Maiduguri to Lake Chad, where Niger, Chad, Nigeria and Cameroon join, cuts through a semi-desert landscape dotted with lonely trees and thatched straw hamlets.
In one village, a skinny old man herds goat across wind-swept sands while a woman in a purple hijab balances a jug on her head, not far from the ashen remains of a car bomb.
Further along, a man in a turban and flowing robes rides on horseback across an expanse of greyish sand, a flashback to the centuries past when Borno was a prosperous sultanate profiting from trade routes crossing the Sahara to the Mediterranean.
Save the odd military checkpoint, there are few signs of statehood here. Disused schools and council buildings decay in dry heat. A fisheries college that was abandoned last year after an attack killed some staff stands eerily empty.
Boko Haram, under the leadership of fiery, gun-toting militant Abubakar Shekau, is thought to be getting closer to achieving its dream of creating some kind of Islamic rule in the lawless areas around Lake Chad, where even the police have fled.
"They are now holding territory," Kole Shettima, chairman of the Center for Democracy and Development, said. "The next step is to create institutions: justice, social services," as Malian Islamists did before the French forced them out of its cities.
The Bama attack showed their substantial firepower, including machine guns, large numbers of rocket propelled grenades (RPGs) and pick-up trucks mounted with anti-aircraft guns, a sign the weapons flood from the Libyan war that helped rebels seize parts of Mali last year has reached Nigeria, officials say.
"They're getting bolder, better armed, more organized. It's looking bleak," a security official in Maiduguri said.
The exact number of Boko Haram fighters is hard to estimate -- and the degree to which Shekau and the four main members of his 'Shura council' -- Habibu Yusuk, Khalis Albarnawai, Momodu Bama and Mohammed Zangina -- have control over them is unclear.
They rarely communicate with the press since their spokesman was killed last year, although Shekau sometimes uploads videos of himself making bellicose statements onto the web.
Security officials believe they have several hundred well-armed and trained fighters and possibly thousands of members.
The army spokesman for Borno state, Lieutenant-Colonel Sagir Musa, denied that the group was staging a significant comeback, but he told Reuters they were moving in bigger numbers than before.
A military convoy rumbles into the remote fishing settlement of Baga, on the shores of Lake Chad, scene of fighting last month that killed dozens of people, many of them civilians.
As it weaves past the charred remains of ruined houses, locals shout abuse at soldiers in the Hausa language.
On April 16, Boko Haram militants armed with guns and RPGs killed a soldier on patrol, slicing his head off with an axe.
What happened next is disputed. Brigadier-General Austin Edokpayi, who heads a multinational force comprising 1,200 Nigerians, 700 Chadians and 300 troops from Niger charged with securing this volatile border area, said reinforcements arrived and met fierce resistance from entrenched Boko Haram gunmen.
Story continues below photo gallery
Pre-violence view of concentration of building damages in Baga (view 1)
Post-violence view of concentration of building damages, as of April 26, 2013. 285 destroyed and severely damaged buildings, burnt trees and fire burn scars visible within this section of Baga.
Pre-violence view of concentration of building damages in Baga (area 2) as of April 6, 2013.
Post-violence view of concentration of building damages (area 2) as of April 26, 2013. 345 destroyed and severely damaged buildings, burnt trees and fire burn scars visible within this section of Baga.
Pre-violence view of concentration of building damages (view 3). Satellite imagery displayed in false-color, near-infrared to highlight areas of extensive fire-related damages and burn scars.
Post-violence view of concentration of building damages (view 3). Extensive fire burn scars, burnt trees and large buildings with intact load-bearing walls without a roof are seen.
Community leaders say the Boko Haram militants had already fled over the border into Chad by the time the soldiers arrived, who then exacted vengeance on the civilian population, shooting, setting fire to houses and killing 185 people.
Whatever the truth of what happened at Baga, Boko Haram's creeping establishment of a stronghold around Lake Chad is becoming a major headache for Nigeria and its neighbors.
"It has emboldened the terrorists," Edokpayi said, complaining that since most local government officials have fled, the military were effectively on their own. "They are eating deep into the ... sovereignty of the Nigerian state."
At one Baga village meeting in which elders complained of heavy handedness by Nigerian troops, an intelligence official told Reuters around half the attendees were Boko Haram members.
Many are poor, young men with little if any formal education and no job prospects in some of the poorest places on earth.
The group's ability to strike fear stems both from its secretiveness — no one who isn't a member can be sure who is — and its visibility in places where the state has withered.
"They are there for everybody to see. You can see them sitting in front of their houses, holding their guns," said a man near Baga fish market who gave his name only as Abubakar.
That Boko Haram is also a menace to other countries around the lake was highlighted in February when it kidnapped a French family of seven from a game park in north Cameroon, taking them over the border into Nigeria. They were freed in April.
The cross border threat is likely to prompt more joint operations. The multinational force was originally set up in 1998 to deal with marauding Chadian rebels, but last year was expanded to include anti Boko Haram operations.
Yet the insurgents' ability to melt away under military pressure and then come back has convinced many that only some kind of political solution will resolve the conflict.
President Goodluck Jonathan set up a body last month to formulate terms for an amnesty, like the one that helped silence militancy in the oil producing Niger Delta in 2009, but the Islamists showed no interest, with Shekau denouncing it.
And few think any peace can hold unless Jonathan's administration can address the underlying causes of insecurity — the North’s extreme poverty and unemployment.
In the meantime, Boko Haram's efforts to revive an Islamist theocracy in northeast Nigeria will cause more bloodshed yet.