Not every Yazidi resident in northern Iraq escaped before the Islamic State, formerly known as ISIS, captured towns in the region. The terrorist group told the people to convert to Islam or die, killed 500 of them, buried some alive, and took hundreds of girls as slaves.

“We have striking evidence obtained from Yazidis fleeing Sinjar and some who escaped death, and also crime scene images that show indisputably that the gangs of the Islamic State have executed at least 500 Yazidis after seizing Sinjar,” said human rights minister Mohammed Shia al-Sudani. “Some of the victims, including women and children were buried alive in scattered mass graves in and around Sinjar.”

“In some of the images we have obtained there are lines of dead Yazidis who have been shot in the head while the Islamic State fighters cheer and wave their weapons over the corpses,” he said. “This is a vicious atrocity.”

The people who did escape received phone calls on Sunday morning with frightening updates. Matthew Barber, a graduate student from the University of Chicago currently in northern Iraq, said people in Hatimiya, Tel Kucho, and Tel Qasab received the threat.

Hearing multiple accounts of a convert-or-die ultimatum given by #IS to 3 #Sinjar villages: Hatimiya, Tel Kucho, Tel Qasab

— Matthew Barber (@Matthew__Barber) August 9, 2014

Can’t confirm, but multiple sources allege deadline for converting to Islam is tomorrow. #Yazidis may die in morning if resisting conversion

— Matthew Barber (@Matthew__Barber) August 9, 2014

Spoke to Yazidi man who received call from daughter in Hatimiya 1 hour ago. She says IS has given them until morning to convert or be killed

— Matthew Barber (@Matthew__Barber) August 9, 2014

Without commander’s approval, #IS guard let man use his phone to bid farewell to family as an “act of mercy.” He is being held w/500 others.

— Matthew Barber (@Matthew__Barber) August 9, 2014

But it is not that easy to convert for ISIS.

But there will be no mercy if he chooses not to convert. And for IS, sincere conversion requires more than saying the shahada.

— Matthew Barber (@Matthew__Barber) August 9, 2014

#IS‘ test for proving sincerity of conversion is “participation in jihad.” To save his life #Yazidi man must convert & then fight his family

— Matthew Barber (@Matthew__Barber) August 9, 2014

In other towns, ISIS slaughtered Yazidis who did not properly convert to Islam. 

WARNING: Graphic images below.

“We are being slaughtered, our entire religion is being wiped off the face of the earth.” http://t.co/buW1wHO6NN pic.twitter.com/RZsidl7o9y

— VICE News (@vicenews) August 7, 2014

Islamic State Executes 67 Yazidis In Iraq For Refusing To Convert To Islam pic.twitter.com/QmhHLdIm1Q

— I’m ur huckleberry (@jeanniemcbride) August 6, 2014

pic.twitter.com/BEajDbCWZu shocking images of Iraqi Yazidis being massacred by ISIS. No international outcry & for them. #TwitterKurds

— Daniel J. Levy (@danielhalevy) August 6, 2014

Those who did escape are suffering in the mountains without food and water. The United Nations said 56 children died from dehydration. Yazidis told Barber what they endured on their flight from IS.

Families described eating leaves to survive, or killing a few animals & eating the meat raw. By now, those still stuck on #Sinjar are dying.

— Matthew Barber (@Matthew__Barber) August 9, 2014

Man relayed to me how an #IS sniper shot his daughter when she ventured out to reach a water source. His eyes were red but tears had run dry

— Matthew Barber (@Matthew__Barber) August 9, 2014

An #IS jihadi drew his gun in the street to kill a father of many children, but his kids gathered around him & the fighter changed his mind

— Matthew Barber (@Matthew__Barber) August 9, 2014

#Yazidi refugee from #Sinjar described to me seeing–with his own eyes–#IS jihadis gun down 2 men & a woman in his street, in broad daylight

— Matthew Barber (@Matthew__Barber) August 10, 2014

On August 7, President Barack Obama announced aid for the refugees and airstrikes against ISIS. Barber and others witnessed people die after an attempt to jump in helicopters.

A man watched two #Yazidi men fall to their deaths after desperately clinging to the landing skids of a helicopter delivering aid in #Sinjar

— Matthew Barber (@Matthew__Barber) August 9, 2014

The helicopter teams are under orders not to do rescues–how do you select 10 passengers from thousands? Yet they haven’t been able to say no

— Matthew Barber (@Matthew__Barber) August 9, 2014

One chopper maxed its carrying capacity with refugees before taking off, but two more men hung onto the underside–both fell to their deaths

— Matthew Barber (@Matthew__Barber) August 9, 2014

#Yazidis who’ve been able to escape #Sinjar tell me that when helicopters dropped food supplies, much of it was destroyed on impact.#Iraq

— Matthew Barber (@Matthew__Barber) August 10, 2014

Islamic State has killed 500 Yazidis, buried some alive http://t.co/cuj4SVthpc pic.twitter.com/9pQcmgZtXG

— Chicago Tribune (@chicagotribune) August 10, 2014

Minority Yazidis in Iraq have been ‘buried alive’ by IS militants as US continues airstrikes http://t.co/OYi9Y5Js7s pic.twitter.com/zxrFviGs86

#Iraq ‘ Yazidis fleeing Sinjar after the Islamic State fighters captured the city and its periphery pic.twitter.com/bML6A4dFTp

— Zaid Benjamin (@zaidbenjamin) August 5, 2014

— Channel 4 News (@Channel4News) August 10, 2014

In July, IS told Christians to convert to Islam, pay a protection tax, or die. The majority chose to leave. The terrorists marked Christian homes and businesses with the letter “N” for Nazarene. IS forced a man to watch the brutal rape of his wife and daughter when he could not pay the tax. This man later committed suicide. Mosul is without Christians for the first time in 2,000 years.