Boko Haram killed at least 60 civilians in an attack on the remote town of Rann in northeast Nigeria earlier this week, Amnesty International said on Friday.
The human rights group's Nigeria director Osai Ojigho said "at least 60 people" were killed while satellite imagery showed "mass burning" of structures used by displaced people.
"Eleven bodies were found within Rann town, and 49 were found outside," the group said in an emailed statement, adding that some 50 people were still missing.
It quoted one of 10 civilian militia members who travelled to Rann to bury the dead as saying the bodies found outside the town all had gunshot wounds.
"This attack on civilians who have already been displaced by the bloody conflict may amount to possible war crime, and those responsible must be brought to justice," said Ojigho.
The death toll made it the "deadliest" by Boko Haram on Rann, she added.
In January 2017, a botched Nigerian air strike intended to hit jihadists killed at least 112 people as aid workers distributed food.
Rann, which is some 175 kilometres (110 miles) northeast of the Borno state capital, Maiduguri, has now been hit four times since March last year.
Rann had been home to some 35,000 internally displaced people (IDPs), according to the International Organization for Migration.
More than 27,000 people have been killed in nearly 10 years of fighting, while some 1.8 million others remain homeless and reliant on aid for food, shelter, healthcare and water.
The UN this week said it needed $848 million (741 million euros) to fund projects for affected civilians in Borno state and two other northeast states over the next three years.
An additional $135 million was required to help the 228,500 Nigerian refugees who have fled to neighbouring Cameroon, Chad and Niger, it added.