For decades a forgotten corner of Mozambique, Cabo Delgado has now become the country’s El Dorado, promising billions in natural gas and gemstones but delivering its population only violence and displacement.

An insurgency in the province now threatens to become further entrenched – 50,000 people have fled their homes since March and Mozambique’s neighbours are currently debating sending in regional forces to help defeat militants who seized a strategic port in the town of Mocímboa da Praia last month.

The fear is that such an action could alienate a population with serious grievances, despite the chaos caused by Isis-linked militant group Ahlu Sunnah Wa-Jamaa, known locally as al-Shabaab (though it has no links with the better-known Somalia-based Islamist militant group of the same name).

Cabo Delgado has spent decades underdeveloped. Even past decade’s dual discoveries of $50bn (£38bn) worth of natural gas and rubies that sell for hundreds of millions of dollars brought only displacement and misery for local people.

“So much is happening around them. One side of them is the al-Shabaab [militants], one side is the government forces also using violence towards them, and on the other side you have the land issue. There’s nowhere to get food, clothes, shelter,” said Estacio Valoi, a Mozambican investigative journalist.

“The issue of violence did not start today or with this conflict. It’s a cocktail.”

Those who have fled Cabo Delgado in the past six months take the total number of people displaced in the region to more than 200,000 (10% of its population) since 2017, when Ahlu Sunnah Wa-Jamaa launched an insurgency. More than 1,000 people have been killed in the past three years.

The latest attacks have added to an already desperate situation for residents, still trying to recover from the destruction caused by last year’s Cyclone Kenneth. More than a fifth of people do not have enough food. Many are forced to seek shelter with relatives and stretch shared resources. Prices for fuel and staple foods such as rice and maize have increased.

The fighting this year has seen many humanitarian groups withdraw from the region. Agencies say they can only access some of the worst areas by air, river or sea, and that rural areas have been all but abandoned because of Covid-19.

Over the past 10 years, local people say the government has forcibly removed whole communities from state-owned land after granting ruby, mining and gas exploration concessions to private companies.

Human rights campaigner David Matsinhe said that in the absence of government services, people have lost access to the land they relied on for food, shelter and income, due to the expansion of mining and gas extraction, while being deemed unqualified for jobs in these new industries.

“They are not only unemployed, they are also unemployable. They are complaining, they have protested against their expulsion [from the land],” he said. “They are saying … it’s only outsiders who come here to benefit and we’re sitting here watching them.”

These grievances had fuelled the conflict more than any influence from international terror groups, Matsinhe said.

“When they speak about the radical preacher coming to radicalise young people, they are forgetting that the government has done for the radical preacher about 80% of the job. He just comes to harvest,” he said.

Last year, the British company Gemfields, owner of the luxury jewellery brand Fabergé, agreed a £5.8m settlement over alleged human rights abuses by security personnel with Mozambicans living in Montepuez, Cabo Delgado’s second-largest city, where the company has a subsidiary. Gemfields recognised that there had been violence before and after it took over the site but denied liability and said it settled in “the interests of the assorted stakeholders”.

Matsinhe said the some of the militants operating in the area were believed to have been from the communities expelled from the mine.

In the weeks since the militants took Mocímboa de Praia, the government has struggled to take back the port, despite its importance to the nearby gas fields. The Southern African Development Community (SADC) regional grouping has considered plans for intervention ranging from intelligence gathering to military support.

The existing military intervention has been led by Mozambican forces, with mercenary groups providing air support, and is accused of inflaming tension through repeated alleged human rights abuses.

Amnesty International last week demanded an investigation into videos appearing to show soldiers torturing and beheading detainees.

Jasmine Opperman, Africa analyst at the Armed Conflict Location and Event Data project (ACLED), said that while regional forces could be required in the military fight against the militants, they could only deliver short-term victories to the Mozambican government.

“The insurgency is reliant on youth dissatisfaction and discontent with the government,” said Opperman. “The SADC cannot and must not think that a military intervention, in isolation from a … project to deal with the root causes, will solve the problem.

“It will create a false sense that the insurgency has been dealt with.”

Inocência Mapisse, a specialist in oil, gas and mining based in the capital, Maputo, said the Cabo Delgado reserves could transform Mozambique’s agriculture-based economy, but that the government was still not investing in the region or its people.

“If we look at the budget for Cabo Delgado province in the last 10 years, it’s the same in terms of the percentage of the [national] budget. It does not change,” she said.

She described it as an El Dorado, promising transformative riches that cannot be accessed because of the fighting over them.

Instead, people displaced in the province have fled massacres by militants and abuses by Mozambican forces.

Médecins Sans Frontières staff who fled a militant attack in May said villagers had to flee into the bush and many children were lost by their families in the panic.

After Mocímboa de Praia’s fall, ACLED documented reports of two women being raped by government forces.

Matsinhe said he was worried about what was happening in villages at the centre of violence, where there is limited or no aid presence and the government has barred the media and researchers.

“It is known that there are people who are not able to run away from the conflict so they are stuck in those areas. It’s practically a death sentence,” he said.