Herianto, a spokesman for Indonesia's Department of Immigration, said 117 Rohingya refugees and 11 illegal fishermen from Myanmar were held in the same area of the detention center in Belawan when fighting began, The New York Times reported.
"There were eight fishermen killed; they are the Buddhists," Herianto said.
He said the 15 injured detainees were Rohingya, a Muslim ethnic group in Myanmar, formerly called Burma.
The detainees used metal and wood from broken chairs to attack one another, Sabarita Ginting, a spokeswoman for Indonesia's immigration office in Medan.
The U.N. High Commissioner for Refugees, in a statement, called for calm among the groups and urged Indonesian authorities to work to prevent more violence.
Widespread violence in the Myanmar city of Meiktila broke out in March following a fight between a Buddhist shopper and a Muslim store owner. Human Rights Watch analyzed satellite images and said more than 800 buildings were destroyed, almost all in Muslim enclaves.