A group of ethnic Rohingya left on a Thai island after a dangerous boat journey from Bangladesh should be given help and the opportunity to determine if they are refugees, Human Rights Watch said Tuesday.

The mostly Muslim Rohingya have long been persecuted in Myanmar. More than 700,000 fled to neighboring Bangladesh in 2017 to escape a military counterinsurgency campaign that the U.S. and others have called genocide. Since then, Rohingya have attempted to leave both Myanmar and Bangladesh on perilous sea journeys to Malaysia, a Muslim-majority country relatively lenient to arriving migrants.

The voyages are often arranged by human trafficking gangs who charge large sums for passage on rickety old boats. Those boats that don't sink can end up elsewhere in Southeast Asia. Thailand, especially, tries to turn them away, usually after supplying fuel and food. Boat passengers who make it ashore in Thailand are detained by authorities or sent by the traffickers to work in slave-like conditions.

The Thai navy said the 59 Rohingya left an island in the Andaman Sea had traveled from Bangladesh on large fishing boats. "But when they arrived, the ship's captain brought these people to the island and said it was Malaysia," the navy's statement said.

The 31 men, 23 women, three boys and two girls were detained after being found Saturday on the southern island of Koh Dong. The navy said it will continue to follow Thailand's standard procedures, including providing humanitarian assistance, for people deemed to be immigrating illegally.

Human Rights Watch said Thailand was obligated to assess the people's claims for refugee protection before trying to return them.

"To protect Rohingya asylum seekers, it is crucial for the Thai government to permit the Office of the UN High Commissioner for Refugees (UNHCR) to conduct refugee status determination interviews," the New York-based group said in a statement.

"The Thai government should end its policy of summarily locking up rescued Rohingya boat people and throwing away the key," said Elaine Pearson, HRW's acting Asia director. "Thailand should permit the United Nations refugee agency to screen all Rohingya arriving in Thailand to identify and assist those seeking refugee status."

In late May, at least 16 Rohingya died after a storm capsized a boat off Myanmar's southwestern coast. There were 35 survivors.

"The risk of abuse at the hands of smugglers and the peril of the sea journey itself are both exacerbated during prolonged journeys, when a safe harbor for disembarkation cannot be found," the office of the U.N. High Commissioner for Refugees said after last month's sinking.