One day in July, Rafiq slipped out of the world's largest refugee settlement, in southern Bangladesh, and crossed the border into Myanmar on a small boat. His destination: a ruinous civil war in a nation that he had fled in 2017.

Thousands of Rohingya insurgents, like 32-year-old Rafiq, have emerged from camps housing over a million refugees in Cox's Bazar, where militant recruitment and violence have surged this year, according to four people familiar with the conflict and two internal aid agency reports seen by Reuters.

"We need to fight to take back our lands," said Rafiq, a lean and bearded man in a Muslim prayer cap who spent weeks fighting in Myanmar before returning after he was shot in the leg.