The jihadist Islamic State is out to exterminate all males perceived as homosexuals in Syria and Iraq, and it uses Facebook to track them down, the head of an international gay rights organisation to the United Nations on Monday.

During a UN Security Council meeting Monday, Jessica Stern, executive director of the International Gay and Lesbian Human Rights Commission (IGLHRC), said ISIS has already killed at least 30 people for sodomy, meaning those who it perceived to be gays.

"We can say that the minimum number of executions for sodomy for which ISIS has claimed responsibility is 30. ISIS-established courts have claimed to punish sodomy with stoning, firing squads, beheadings, and by pushing men from tall buildings," Stern said said.

Subhi Nahas, a gay refugee from Syria, said the persecution of gays in Syria began even before ISIS, reports said.

He said President Bashar Assad's government "launched a campaign accusing all dissidents of being homosexuals" when uprising started in 2011. He added that gay hangouts were raided and people were arrested and tortured.

"Some were never heard from again," he said.

When the al-Qaeda linked Nusra Front took over the Syrian town of Idlib in 2012, militants warned that "they would cleanse the town of those involved in sodomy," he said. Homosexuals were then arrested and executed, Nahas said.

When ISIS seized the city last year, the violence against homosexuals worsened, he said.

"At the executions, hundreds of townspeople, including children, cheered jubilantly as at a wedding," Nahas said. "If a victim did not die after being hurled off a building, the townspeople stoned him to death. This was to be my fate, too."

Nahas managed to escape to Lebanon, where he left for Turkey and finally the United States.

Adnan, an Iraqi, said he suffered from brutality under Iraqi security forces even before the ISIS came.

He said ISIS militants "are professional when it comes to tracking gay people. They hunt them down one by one. When they capture people, they go through the person's phone and contacts and Facebook friends."

"They are trying to track down every gay man. And it's like dominoes. If one goes, the others will be taken down, too," he said.