Villagers are fleeing a gas-rich region in northern Mozambique and energy giants are pleading for more protection in the face of mounting attacks by a shadowy jihadist group.

Security officials and local residents interviewed by AFP described a bushfire of fear spreading in Cabo Delgado, Mozambique's northernmost province, and plummeting morale among troops and police.

The organisation first came to light in October 2017, targeting a police station.

Since then, the group has killed more than 700 people, according to the medical charity Doctors Without Borders (MSF).

The UN says at least 100,000 people have fled their homes and violence is spreading towards the province's south.

"There has been a dramatic increase of brutal attacks by armed groups over the past months, with the recent weeks being the most volatile period," UN refugee agency spokesman Andrej Mahecic said this month.

Civilians are fleeing "in many directions, including to small islands, where many have nowhere to stay," he said.

The group is known locally as "Al Shabaab, "athough there is no discernible connection with the notorious Somali jihadist organisation of that name.

Since June, the so-called Islamic State group has claimed around 20 attacks in Cabo Delgado, saying these targeted the Mozambican army.

But analysts say they know of no evidence of IS financial or military support to the Mozambican jihadists.

- Exodus -

Grassroots sources in the region confirm the worsening situation.

MSF's teams in the area "have witnessed lines of people walking on main roads as their villages go up in flames," said its coordinator there, Bruno Cardoso.

"Here in Macomia (district) we are all in a panic. The situation is one of great fear," a police officer told AFP by phone.

"Many children don't come to class," said a teacher at a Macomia primary school. "We live in... deep fear."

The militants are operating on the doorstep of energy majors, including Exxon-Mobil and French oil company Total, which are preparing to extract gas in the Rovuma basin off Cabo Delgado's coast by 2022.

With more than $30 billion in investment sunk into the project, President Filipe Nyusi Nyusi is under pressure to respond.

Last week he skipped the African Union's bi-annual summit in Addis Ababa and held a cabinet meeting in Cabo Delgado's capital Pemba -- one of the rare occasions in which he has hosted the weekly meetings outside Maputo. He blamed the "war" on unnamed "foreigners".

The oil giants have asked for the doubling of the 500 soldiers deployed in April to guard a liquefied natural gas (LNG) facility at Afungi, one of Africa's biggest single investments in Africa.

Ryan Cummings, an analyst with Cape Town-based Signals Risk, said there had been a shift in the frequency and style of attacks.

They now targeted not only civilians but also the security forces, whose counter-terrorism capability is questionable, he said.

"That could portend an evolution or sophistication in their modus operandi," Cummings said.

"(This) would be especially concerning for the foreign multinationals that are engaged in the LNG industry in the Rovuma basin."

Defense Minister Jaime Neto said the authorities would provide protection.

"We have enough staff and we guarantee the security of the projects," he said.

- Low morale -

But the security forces are themselves despondent, according to internal sources.

"We do not have the capacity to intercept the jihadists communications (and) that is why we don't know the enemy's capacity," an agent from the police rapid response unit told AFP.

The unit opts to not respond to attacks on villages "to avoid casualties in our ranks".

An agricultural college was recently raided and looted "and we didn’t respond, we feared we were outnumbered", said the agent.

Another police officer said militants stole a police van in December and have been using it to stage attacks.

A special operations police commander in Maputo told AFP "many young (military recruits) abscond" if they are posted to Cabo Delgado.

"The situation is chaotic. Troops on the ground opt for defensive. Now it is the jihadists who are chasing and attacking government troops and not the opposite.

"Our big problem is the lack of resources," he said.