It's been called the "crime of crimes" and it has put three-quarters of the world in the dark.

Like a plague, persecution of Christians is getting worse, with up to 75 percent of the world's population now living without religious freedom, European Union's special envoy Jan Figel said.

Speaking on Premier Christian Radio on Thursday to mark International Freedom of Religion or Belief Day, Figel said the majority of the world's population continues to lack freedom of religion or belief.

"Therefore, those who believe that humanity should prevail can, and should do, much more for freedom of religion," Figel said. "We are witnesses of a systematic and mass murder, martyrdom and persecution on several territories."

According to the Christian persecution watchdog group Open Doors, more than 7,000 Christians were killed for their faith from Nov. 1, 2014 to Oct. 31, 2015. That number is over 3,000 more than those killed for faith-related reasons in the previous reporting period (2013 to 2014), The Christian Post reported.

Moreover, over 2,400 churches were attacked, damaged or destroyed during the latest reporting period, which is more than double the number from the previous period..

"This crime of crimes is calling for all serious people to do more," Figel pointed out.

The rise in Christian persecution cases is attributed to the spreading tentacles of Islamist extremist groups like the Islamic State (ISIS), Boko Haram and Al-Shabaab in the Middle East and Africa.

"Islamic extremist caliphates are solidified and expanding," Open Doors USA President David Curry said earlier. "The data shows that the Islamic State caliphate has effectively carried out genocide against Yazidis and Christians in Syria and Iraq, pushing hundreds of thousands of Christians into refugee camps in North Iraq and other countries."

ISIS currently controls parts of Iraq and Syria but is still seeking to expand its so-called caliphate to include most of the Middle East.