Nahas told his experiences of life under IS at an informal closed-door meeting of the Security Council on Monday
Nahas told of how the Nusra Front took over his hometown of Idlib and begun torturing and executing men suspected of being gay. When IS took over they begun throwing men suspected of being gay from rooftops and stoning them if they remained alive.
"I was terrified to go out. Nor was my home safe, as my father, who suspiciously monitored my every move, had learned I was gay. I bear a scar on my chin as a token of his rage," said Nahas.
Nahas fled Syria to Lebanon, then moved to Turkey.
"Death threats followed me to Turkey. A former school friend from Idlib named Khalil had joined (Islamic State). He relayed through a mutual friend that he wanted to kill me, aiming to go to paradise," he said. "I was terrified."
Islamic State has declared a caliphate in territory it has seized in Iraq and Syria.
U.S. Ambassador to the United Nations Samantha Power said this was the first time the U.N. Security Council had discussed lesbian, gay, bisexual and transgender issues.
"Today, we take a small but important step in assuming that work. It must not be our last step," she said.