More than 20 people, including an 11-year-old boy, were hurt in the attack Thursday, Aftenposten reported. The victims were Arabs and Kurds and the BBC reported the attack may have sprung from arguments about Muslim religious practices.

The Nordbybrathen transit center is at Valer southeast of Oslo.

Morten Tjessem, general secretary of the Norwegian Association for Asylum Seekers, said that the residents of the Valer center are under stress because their claims have been rejected and they are waiting to be deported to their home countries.

"Conflicts are not uncommon in a situation like this but a large group of people coming in from outside is both unusual and shocking," Tjessem told the BBC.

Police said that estimates of the number of attackers varied widely from 40 to 100. Some residents reported seeing firearms but investigators have found only iron bars and machetes, the BBC said.

Two of the suspects came out of the woods near the center. Others were arrested nearby.