Ngouboua - Boko Haram militants driven out of strongholds by a regional military offensive are increasingly taking refuge on remote islands in Lake Chad, terrorising locals or recruiting others.
The lake is where borders meet for Nigeria, Chad, Cameroon and Niger, which are leading the fight against the extremists and their bloody six-year insurgency that has prompted an armed international response.
"You see those islands, toward Nigeria? I used to go there to sell my harvest," said Mustapha, a farmer from Ngouboua, a Chadian village near the border with Nigeria.
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"But with Boko Haram it's become too dangerous. We don't move without a military escort," he added.
Though the military - with major help from its neighbours - has since February retaken a series of towns and villages held by the rebels, the insurgency that has left 13 000 dead has not been crushed.
Theft of cattle, rice and corn
Some of the fighters scattered by the government victories have instead fallen back to the sanctuary of remote or inhospitable areas around the lake.
"Boko Haram are under pressure and some of them are taking refuge in the middle of the lake," on islands with swampy forests that are difficult for the army to reach, said a Chadian security source.
"Because they are hungry, they are attacking villagers for food," the source added.
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The theft of cattle, rice and corn have become common on the Chadian islands and mainland near Nigeria. Boko Haram fighters have been blamed for at least two attacks on a village near Chadian market town Tchoukou Telia.
"They stole up to 500 steers," said Al Hadji Mbodou Mai, a shopkeeper in Ngouboua.
That town was victim of Boko Haram attacks in recent months, but now is "secured" by a heavy military presence, said local police commander Saleh Ali.
"There are a lot of problems on the surrounding islands," he added.
Fighting the Islamists in the remote, swampy areas is sure to get more difficult when the rainy season arrives in June.
Also, experts have warned that hit-and-run attacks by the group could increase amid the added military pressure.
The aggressive campaign against Boko Haram came ahead of elections that saw incumbent President Goodluck Jonathan, often criticised for his failure to stamp out the insurgency, fighting a close re-election race he ended up losing.
President-elect Muhammadu Buhari, who does not take charge until late May, has already vowed to be a more effective commander-in-chief than Jonathan, in part by ensuring that the military is properly funded and equipped.
Authorities in Chad are also worried about signs that locals are being recruited to help and even fight alongside the insurgents.
Chadian Boko Haram members were blamed for an ambush that left seven civilians dead on Friday, some with their throats cut. According to a local official the victims were killed after rebuffing the Islamists' recruitment efforts.
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However, authorities do not have a clear picture on the number of Chadians who have taken up arms for Boko Haram and what is motivating those who have done so.
In the span of a month about 30 suspects were arrested around Ngouboua on suspicion they were informants for the Islamists, police said. Most of those taken into custody were motorcycle taxi drivers.
Authorities have also picked up for questioning young men who disappear from their families for days at a time.
"We interviewed a boy who was hardly 16 and who has spent two weeks in a camp at the border... He was promised money, but especially Tramol," the source said, referring to a pain medication popular among poor local youths.
"The authorities try to deal with the problem by talking with their parents and making them understand there be any trouble if the boys come back," the source said.