For more than two years the fighters waged a war so shadowy no-one really knew why they were fighting or even what they called themselves.
They seemed to come out of nowhere, bands of masked men who attacked villages in northern Mozambique’s Cabo Delgado province, carried out mass beheadings and then vanished as mysteriously as they had appeared. Up to 1,000 soldiers and civilians have so far been killed by the group.
Then, in the past few weeks, everything changed.
No longer masked, the militants seized important towns and villages in a series of sophisticated operations launched under the noses of a Kremlin-linked Russian mercenary outfit.
Unfurling the black flag of Islamic State in southern Africa for the first time, the fighters defiantly declared their intention to turn a region that will soon be vital to Britain’s energy security into a Sharia-based caliphate.
Until recently, Cabo Delgado’s insurgency had garnered little attention in Western capitals.
For many politicians, it seemed to be just another obscure conflict taking place in a chronically corrupt country with a long history of violence.
But the latest attacks and the threat they potentially pose to what is becoming one of the world’s most important gas regions are causing a rapid and urgent reassessment.
Until recently, the violence in Cabo Delgado had indeed seemed like a local affair.
True, the group responsible for it had initially been dominated by foreigners, radical east African Muslims who fled down the Swahili coast after their leader, Aboud Rogo, was killed by police in Kenya in 2012. But they were rapidly able to find adherents among the local population.
Cabo Delgado should be one of the richest regions in Africa. Not only does it boast the world’s largest ruby mine, it is home to a £44bn liquefied natural gas (LNG) programme — the continent’s largest ever energy project — that is being developed by some of the world’s biggest oil companies.
With investment in the LNG project set to double over the coming decade, Cabo Delgado is turning Mozambique into an energy superpower, one of the ten largest producers of natural gas in the world.
As Britain’s North Sea reserves dwindle, the UK is among those queuing up for a share of the region’s resources. Last year Centrica, the parent company of British Gas, entered into a joint venture to buy 2.6m tonnes of LNG from Mozambique a year for the next two decades.
The mostly Muslim population of Cabo Delgado has seen little of the wealth, however. The region is by far the least developed in Mozambique and its 2.3 million people the poorest, making some ripe for recruitment.
As its ranks swelled, the group — which operated under a series of names, most commonly Ansar al-Sunna — grew steadily bolder after launching its first attacks in 2017, culminating in its apparent adoption into the ISIL franchise at some point in the past six months.
Increasingly worried by the group’s growing capability, Mozambique’s government last year deployed 200 Russian mercenaries to Cabo Delgado from the Wagner Group, believed to be owned by Yevgeny Prigozhin, a businessman with close ties to Vladimir Putin.
Although the Russians arrived with attack helicopters, drones and sophisticated weaponry they were swiftly forced to make a “tactical retreat”. As many as 12 Russians have been killed, according to diplomats.
Success against the Russians seems to have emboldened the militants further.
From mid-March the number of attacks has surged.
In the most significant, militants marched into the port of Mocimboa da Praia on 23rd March and seized control of the town. Although they marched out 24 hours later — replicating a tactic used by al Shabaab in Somalia and Isil fighters in the Middle East — they had made their point. Mocimboa da Praia is just an hour’s drive from gas fields.
Amid a collapse in oil prices and economic uncertainty unleashed by the coronavirus pandemic, the escalation in the insurgency is making western energy companies increasingly anxious.
The reaction to the jihadist occupation of some towns, with many locals coming onto the streets to cheer, will do little to allay their nerves.
It is difficult to tell how genuine the support is. Stepping up their public relations campaign, the Islamists have sought to woo people by distributing stolen food and blowing up cash machines to dole out banknotes.
But support may also be rooted in fear. “We don’t want to hurt you,” a militant leader told residents in one captured town, according to video footage. “If you do not report us to the police, we will live with you.”
“But if you denounce us and tell the pigs where we are hiding, the next time we come here we will kill everything, even chickens and eggs, old people and babies.”
The threats, Western officials say, are working because neither locals nor the energy companies have any confidence in the ability of the underpaid and demoralised security forces to stand up to the jihadists.
Instead of fighting when towns were attacked, many soldiers and police officers have been ditching their uniforms and blending into the civilian population, locals say.
Few therefore believe Mozambique’s national police commander, Bernardino Rafael, who claims that the situation in Cabo Delgado is under control and the insurgents are merely a handful of “criminals” who will soon be dealt with.
“When armed men come, instead of defending the population, the police flee,” said Viana Magalhaes, a senior opposition politician. “If a group of insurgents can take control of a whole province, then the country has no protection.”