Modeste Bakwanamaha told The Associated Press that one inmate had died in the attack on Kangbayi prison in the eastern city.
“We call on the population to report any suspicious person who may be an escaped prisoner,” he said.
The mayor said that 20 of the escaped prisoners had already returned, preferring incarceration to life with the rebels.
“Those who came back say that they were taken by force. They say they had to escape from their abductors, the ADF, because they did not want to live as enemies in the bush,” said Mr Bakwanamaha.
We call on the population to report any suspicious person who may be an escaped prisoner
News of the Kangbayi escape angered locals, who feared it could further exacerbate violence in the area.
“It is a danger to the community of Beni,” said resident Sadi Amundala. “We would like our government to improve the conditions of life in prisons and also strengthen the police and military presence to prevent future escapes.”
The escape comes three years after another attack on the Kangbayi prison in which about 100 inmates had fled and dozens were killed.
The Allied Democratic Forces (ADF) rebel group originated in Uganda and has long been operating in eastern Democratic Republic of Congo.
The so-called Islamic State group on Tuesday claimed responsibility for the prison attack in an announcement on its Amaq news agency.
