GENEVA — The authorities in Papua New Guinea have vowed to use force, if necessary, to remove hundreds of migrants and refugees protesting at a closed detention center on the remote Manus Island if the men have not left of their own accord by Saturday.

Conditions have deteriorated in recent days for the nearly 600 men, mostly from the Middle East and Southeast Asia, who were sent to the island as part of Australia’s offshore detention program. Some have been held there for years.

United Nations experts on Thursday said that Australia was responsible for the developing humanitarian crisis, urging the government to move the men to safety in Australia and to end its policy of sending asylum seekers to offshore centers.

The United Nations Human Rights Committee, a panel of independent experts, bluntly rejected Australia’s position that it had no obligation toward the welfare of migrants it had sent to the center because they were not on Australian soil.