More than 1,200 people have died of starvation and illness at an aid camp in north-east Nigeria that houses people fleeing the Islamist militant group Boko Haram, according to the medical charity Médecins Sans Frontières.

MSF said on Thursday that its team found 24,000 people, including 15,000 children, sheltering in the camp located on a hospital compound during a visit to Bama last month – its first trip there since the city was wrested from Boko Haram’s control in March 2015.

Bama was part of an area held by Boko Haram for more than six months before the group was pushed out by the army.

MSF said a “catastrophic humanitarian emergency” was unfolding at the camp. It said around a fifth of the 800 children who underwent medical screening were acutely malnourished and almost 500 children had died.

“We have been told that people including children there have starved to death,” said Ghada Hatim, MSF’s head of mission in Nigeria. “We were told that on certain days more than 30 people have died due to hunger and illness.”

During its assessment, the MSF team counted 1,233 graves near the camp that had been dug in the past year. It said 480 of the graves belonged to children.

More than 15,000 people have been killed and 2 million displaced in Nigeria and neighbouring Chad, Niger and Cameroon during Boko Haram’s seven-year insurgency, in which the group has tried to create a state adhering to sharia law.

Nigeria’s army, aided by troops from neighbouring countries, has recaptured most of the territory that was lost to the group. But the jihadi group, which last year pledged loyalty to Islamic State, still regularly stages suicide bombings.