The men with the guns arrived in Moda early on a Sunday morning. There were only a dozen of them, but they were enough to send the villagers fleeing for their lives. Now, two years later, most of those who fled have come back, to find their homes destroyed, their livestock gone and their fields ruined.

They are among the more than three million people in north-east Nigeria who were displaced in what has become one of the world’s worst – and least reported – humanitarian disasters. The UN has warned that up to 75,000 children could die within the next 12 months unless more help arrives urgently.

The villagers are the invisible victims of a jihadist insurgency by Boko Haram, the same Islamic extremist group that in April 2014 abducted more than 270 schoolgirls from the town of Chibok, 100 kilometres west of here. They are invisible because once they left the camps where they had been sheltering, officials assumed that they would be able to cope without further assistance. Only now is it becoming clear that returning home has brought no improvement in their living conditions and a major international effort to save them is swinging into action.

The UN and other agencies are urgently appealing for additional funding to help the forgotten victims of Boko Haram. The children’s agency Unicef has raised barely a quarter of the $115m it says it needs.

With the world’s attention fixed on the crises in Syria and Yemen, as well as on the domestic political upheavals in the US and Britain, the UN’s humanitarian co-ordinator in Nigeria, Peter Lundberg, says the crisis here is worsening rapidly. As many as 14 million people could soon be in need of help; an international funding conference is to be held in Geneva next month.

Unlike the refugees from Syria and elsewhere, whose perilous journeys to Europe have rarely been out of the headlines, the people of north-east Nigeria have remained almost entirely below the media radar.

Even in Nigeria, there has been little coverage of their plight and with the country’s economy now in recession for the first time in 25 years, mainly because of the collapse in oil prices, the government has been unable to allocate enough resources to provide the food and other aid that they need.

Here in Moda, a dirt-poor village of about 500 families close to the border with Cameroon, Annina Dahiru said she and her five children used to have enough food. But that was before the men with the guns came. She, her husband, and their children fled on foot when the village was attacked, but in the panic she and her husband were separated. She never saw him again and has no idea if he is alive or dead.

We sit in the shade of a neem tree – the oil from its seeds can be used in the production of cosmetics, soap and detergents – and with her youngest daughter, one-year-old Fatima, cradled in her arms, Annina says: “Life is nothing like it used to be. Now we never have enough food.” The Boko Haram fighters blew up her house after she and her family fled; when she returned, her brothers managed to scrape together just enough money to enable her to build a single room for herself and her children.

The situation is likely to get worse before it gets better. More people will return home and find there's nothing there Pauline Bannaman, Oxfam

Pauline Bannaman of Oxfam, which provides water, sanitation and hygiene assistance in the area, as well as small cash handouts to enable villagers to buy food in local markets, says: “We think the situation is likely to get worse before it gets better, because large areas are now opening up after the military campaign against Boko Haram, which means that more people will be returning to their homes and finding nothing there.”

In Borno state, where the insurgency began seven years ago, the medical relief agency Médecins sans Frontières says thousands of children have already died of starvation and disease. According to the agency, a survey conducted in two camps for displaced people in Maiduguri indicated that mortality rates among children under the age of five were more than double the threshold for the declaration of an emergency.

In the city of Yola, capital of neighbouring Adamawa state, more than 700 people are still sheltering in the grounds of the catholic St Theresa’s cathedral, refusing to leave until they are given cast-iron guarantees that it is safe to do so. At the height of the crisis, the church was providing for more than 3,000 people, although most of them have now returned to their homes.

Father Maurice Kwairanga, who runs the cathedral’s programme for displaced people, said: “Many places are still not as secure as the media or the military say they are. Close to the highways it may be OK, but not in the more isolated rural communities where there is no security cover. Some people from here did go back home, but they were then attacked and came back here to the cathedral. So we are going to have to continue to make provision for them for as long as their homes are not genuinely safe.”

Facebook Twitter Pinterest Children playing in the compound of St Theresa’s Cathedral. Photograph: Robin Lustig for the Observer

In the dust of the cathedral compound, children squealed happily from within a makeshift playground. Nearby, women were sifting groundnuts before grinding them into a paste with which to fill empty stomachs. One woman, whose husband was killed by Boko Haram fighters when they came to her village, said: “I have heard that now there is peace there, because the military are there. My children keep asking when we are going home, but I still fear that we could be ambushed.’

The Nigerian army has pushed Boko Haram back from much of the territory in the north-east of the country that they used to control. But the civilian authorities have been accused of being too slow to help the victims of the military campaign and to rebuild infrastructure damaged during fighting. On the main highway between Yola and Michika, we had to negotiate a blown-up bridge, destroyed by the military to halt Boko Haram’s advance on the state capital.

Sa’ad Bello, head of operations at the National Emergency Management Agency in Yola, denied that the authorities had delayed organising assistance.

“The situation is improving,” he said. “People are returning to their homes voluntarily and all parts of Adamawa state are now in government hands. We continue to provide assistance as we have done since the inception of the crisis.”

The rise and fall of Boko Haram

Boko Haram, translated by many as “no western schooling”, is a Sunni Islamic fundamentalist sect advocating a strict form of sharia law. It was formed in 2002 by Mohammad Yusuf, a Nigerian who studied theology at the university of Medina in Saudi Arabia.

The group, once considered the world’s deadliest terror organisation, was reported to have links with al-Qaida, but in March 2015 announced its allegiance to Islamic State. Active mostly in north-east Nigeria, it also operates in Chad, Niger and Cameroon. Targets are mainly churches, mosques and often the poorest of villages.

Since the major Boko Haram uprising began in 2009, during which Yusuf was captured and executed, its fighters have killed more than 20,000 people and displaced 2.3 million from their homes.

In April 2014, the kidnapping of 276 girls from a secondary school in Chibok brought the group to international prominence and spawned the global Bring Back Our Girls campaign. Following the death of Yusuf, Boko Haram has been led by Abubakar Shekau, who has been reported dead with regularity, most recently in August 2016.

In 2015, the group, weakened by advances of the Nigerian army, was declared “technically defeated” by President Buhari. It has since split, with a rival faction under Abu Musab al-Barnawi, whom Isla mic State claims is leader of its west African branch.