NEW YORK (Thomson Reuters Foundation) - Genital surgery should be banned on children whose sex characteristics are ambiguous because the procedures can scar young patients for life and be considered human rights violations, a leading rights group said on Tuesday.

Several hundred so-called intersex children in the United States have undergone sex reassignment surgery in recent years, and worldwide, doctors recommend surgery for an estimated one in every 2,000 intersex babies, U.S.-based Human Rights Watch (HRW) and interACT, an advocacy group, said.

Surgeries to make them resemble more typical boys or girls include removal of testes or ovaries, deepening shallow vaginas and enlarging small penises, they said in a report.

They called for a U.S. moratorium on all surgical procedures on intersex children too young to participate in the decision.

The surgeries amount to “human rights abuse taking place in a medical setting,” said Kyle Knight, a HRW researcher.

“These surgeries are medically unnecessary, they are harmful and they haven’t delivered on the outcomes that were originally theorized,” he told the Thomson Reuters Foundation in a telephone interview.

The report said the benefits of sex reassignment surgery remain unproven but the resulting harm can be catastrophic.

Surgery can cause life-long pain, sterilization, loss of sexual sensation and health complications, it said.

Some 1.7 percent of the world’s population, or 127.5 million people, is thought to be born intersex, according to the report.

But detailed data on the U.S. intersex population, once called hermaphrodites, is largely lacking, Knight noted.

The surgeries’ popularity dates back to 1960s’ research which concluded intersex people could be assigned typical male or female genitals if operated on early in their infancy, HRW and interACT said.

In a recent open letter cited by the report, three former U.S. Surgeons General said plastic surgeries on genital organs “can cause . . . emotional distress.”

Efforts to warn medical doctors about the risks have been ongoing since the 1990s but met with mixed success, the report said.

It did find that a growing number of doctors are opposed to recommending surgery on intersex babies unless medically necessary, the report said after interviewing nearly two dozen health care practitioners.

Various United Nations’ agencies have condemned the practice as violating fundamental human rights.

In 2015, Malta became the first nation to ban non-consensual medically unnecessary surgeries on intersex children.

Belgian fashion model Hanne Gaby Odiele put a public spotlight on the issue earlier this year when she revealed she was born intersex.