The world is "largely silent" about the "genocide" being committed by Islamic State against Christians, Yazidis and other religious minorities, according to Franklin Graham.

The Samaritan's Purse founder and son of famed evangelist Billy Graham has been outspoken in his support of minorities in Iraq and Syria – and also in his attacks on Islam.

In a Facebook post yesterday Graham said that Islamic State's methods were "unimaginably cruel and heinous". He referred to the murder of three Assyrian Christians on September 23 and to that of 12 others the previous month, as well as to the crucifixion of a 12-year-old Christian boy.

"On that same day, ISIS militants publicly raped two Christian women in front of a crowd and then beheaded them along with six others when they refused to convert to Islam."

He referred to a Fox News report that said, "They have every intention of spreading that bloodshed around the world, including America."

Graham concluded, "Pray for an end to this horrendous evil in the name of religion."

Graham has been severely critical of Islam and has cast doubt on its claim to be a religion of peace.

He condemned President Obama's suggestion at February's National Prayer Breakfast that Christians were capable of violence in the name of religion in a succession of tweets, saying: "Jesus came to give His life for the sins of mankind, not to take life. Mohammad was a warrior and killed many innocent people." He concluded: "True followers of Christ emulate Christ – true followers of Mohammed emulate Mohammed."