Aid agencies including the UN children’s fund, Unicef, are profiting from money meant to help those fleeing Boko Haram’s Islamic uprising and should leave the country, according to the governor of Nigeria’s north-eastern Borno state.

The comments by Kashim Shettima came as agencies warned of severe hunger and accused the government of underplaying the crisis.

Shettima made the remarks to legislators and journalists on Tuesday in Maiduguri, the state capital and birthplace of Boko Haram’s Islamic insurgency.

His criticism followed similar observations by President Muhammadu Buhari, who in December accused the UN and private agencies of exaggerating the humanitarian crisis to boost funding.

Meanwhile, Nigeria’s Senate is investigating accusations that government agents are stealing food aid. On Monday, several officials with the Borno State Emergency Management Agency were charged with theft after camp guards allegedly caught them loading vehicles with dozens of bags of rice from a store at a refugee camp.

The UN launched an appeal in December for $1bn (£823m), warning that 5.1 million people faced severe hunger in north-east Nigeria and tens of thousands of children would die without critically needed aid.

Shettima said the state had become “a cash cow”, with people profiting “from the agony of our people”.

“People that are really ready to work are very much welcome here,” he said. “But people that are here only to use us to make money may as well leave.”

He said only eight of 126 registered agencies were doing “good work”, including the World Food Programme and UN Population Fund, the International Committee of the Red Cross, the International Organisation for Migration, the Norwegian Refugee Council and the Danish Refugee Council.

Shettima accused Unicef of misusing funds by buying bullet-proof vehicles. Such a vehicle saved lives in July when Boko Haram attacked a military-escorted humanitarian convoy, wounding a Unicef worker, two other aid workers and two soldiers.

Unicef said funding requirements were based on the needs of 8.5 million affected by the crisis in north-east Nigeria, including 4.4 million children. Insecurity had initially made it difficult to reach many affected areas, said a spokesperson, but last year the organisation reached 160,000 children under five with life-saving treatment in Borno, Yobe and Adamawa states.

“Until April 2016, most of Borno was inaccessible to humanitarian agencies because of insecurity. As security conditions on the ground improved, Unicef and its humanitarian partners have greatly scaled up our work in previously inaccessible parts of the state,” said the spokesperson.

“Many areas remain dangerous, however, and the safety of Unicef staff working in these highly challenging conditions is of great concern.”

Unicef’s latest situation report said the agency treated 160,000 children under five for severe acute malnutrition in 2016, helped to provide healthcare for 4.2 million in the war zone, brought clean water to 745,000 people and provided more than 1 million people with hygiene kits and education.

The organisation predicts that one in five of the estimated 450,000 children at risk of severe acute malnutrition in 2017 will die without treatment. Less than half of the $115m requested for the crisis in 2016 was received, said Unicef, adding that “lack of funding continues to limit the effectiveness of our response”.

Last year, Shettima accused rival politicians of instigating protests by refugees from Boko Haram who said they had received no food aid for weeks. Shettima was publicly booed by refugees and residents, with some shouting “Rice thief!” when his convoy passed.

Shettima said on Tuesday that while the government has been focused on resettling refugees and reconstruction, aid agencies are concentrating on refugee camps, which his government wants to dismantle by May. Aid agencies have warned against the hasty resettlement of refugees in towns and villages still vulnerable to attack by Boko Haram.

Tensions between the Nigerian government and aid agencies have increased, with agencies accusing the government of trying to hide the extent of the crisis.

Médecins Sans Frontières said last week that it has stepped outside its traditional medical role to distribute food because people are “in desperate need” and other organisations are not stepping up.

Aid agencies have warned that many more people could die in addition to the more than 20,000 killed in the seven-year Islamic uprising that has driven 2.6 million people from their homes and, in some cases, across Nigeria’s borders.