SYDNEY, Australia — Australia and Papua New Guinea have failed to protect hundreds of asylum seekers sent to Manus Island under Australia’s contentious offshore processing policy, and threats to their safety and health will increase if Australia closes the island’s main detention center next week as planned, Human Rights Watch said on Thursday.

In a report based on interviews with 40 of the 770 refugees and asylum seekers on Manus, which is part of Papua New Guinea, Human Rights Watch investigators said that several had been assaulted or robbed by local young men, who in some cases were drunk and armed with knives or screwdrivers.

At least three victims since June required emergency medical attention in Papua New Guinea’s capital, Port Moresby, or in Australia, according to the report, which said that in most of the cases no one was charged or punished.

“There has been an escalation in violence in the last six months and there has been little to no action by police,” Elaine Pearson, the Australia director at Human Rights Watch, said in an interview. “It’s simply not safe to move them out of the facility.”