SALMON, Idaho (Reuters) - An Idaho prosecutor said on Wednesday that internet outlets devoted to carrying anti-Muslim sentiments were to blame for fomenting widely spread, false rumors that three Syrian refugee boys had gang-raped a young girl at knife-point.

“There was no gang rape, there were no Syrians involved and there was no knife. None of it is true,” Twin Falls County Prosecutor Grant Loebs said of the reports, which originated on blogs and social media postings and have since gone viral.

He told Reuters those reports stemmed from an incident on June 2 in which three boys - aged 7, 10 and 14 - were accused of assaulting a 5-year-old girl in an apartment house laundry room in the southern Idaho city of Twin Falls.

An investigation by Twin Falls police found one of the boys sexually assaulted the girl and the two others were involved in the crime but did not touch the child, Loebs said.

Two boys were charged in the case, which an Idaho court has been sealed because they are minors, and were being held in a juvenile detention facility, the prosecutor said.

Twin Falls Police Chief Craig Kingsbury, accused by anti-Muslim groups of a cover-up, said publicly that one of the boys was from Sudan, the other from Iraq. He added they had been in the United States for less than two years, but their immigration status was not immediately known.

Anti-Muslim agitators and those opposed to resettlement of refugees from the Syrian civil war nevertheless seized on the incident to buttress their arguments for shutting down a refugee center in Twin Falls to prevent entry by displaced Syrians.

“They are not compatible with our culture. They hate us. They don’t want to be Americans,” Vicky Davis, a local citizen opposed to the refugee center, said during a City Council meeting on Monday night.

The controversy flared as Donald Trump, the presumptive Republican presidential nominee, escalated his anti-Muslim rhetoric after last week’s deadly mass shooting at a gay nightclub in Florida by a gunman pledging his allegiance to Islamic State militants.

Trump has called for a blanket ban on Muslim immigrants and heavier government scrutiny of mosques.

Ibrahim Hooper, spokesman for the Washington-based Council on American-Islamic Relations, said the Idaho sexual assault should be fully investigated but added the case had become a lightning rod for anti-Muslim, and anti-refugee sentiments.

“These two forms of hostility seem to be overlapping and reinforcing each other,” he said.