Rohingya refugees who have fled ethnic violence in Myanmar are at risk of “a humanitarian crisis within the crisis” as the impending cyclone and monsoon seasons threaten to flood camps and fuel the spread of disease, diplomats at the United Nations Security Council warned on Tuesday.

More than 100,000 refugees living in makeshift camps in Bangladesh are in areas prone to flooding and landslides, and tens of thousands will have to be relocated before the high waters hit in March, said Filippo Grandi, the United Nations high commissioner for refugees.

“Their lives are greatly at risk,” Mr. Grandi said.

Though the stream of refugees pouring over the border into Bangladesh has abated somewhat, the Rohingya, a long-persecuted Muslim minority predominantly in western Myanmar, continue to flee their homes. About 1,500 have already arrived in Bangladesh this month, bringing with them reports of continued violence by Myanmar’s authorities, including the abduction of girls and young women, enslavement and forced starvation, said Masud Bin Momen, Bangladesh’s ambassador to the United Nations.

Calling the Rohingya the “most persecuted minority in the world,” Mr. Bin Momen said that despite an agreement between Bangladesh and Myanmar for the voluntary repatriation of the refugees, most do not feel safe enough to return home, even if they have homes to return to.