(CNSNews.com) – Nine of the 10 countries with the worst records for persecution of Christians have populations that are at least 50 percent Muslim, according to the assessment of persecution in the Open Doors USA's World Watch List (WWL) 2015 and population information published by the State Department and the Central Intelligence Agency.

The WWL is an “annual survey of religious liberty conditions for Christians around the world" that was released Wednesday.

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Communist North Korea topped the list for the 13th consecutive year for the regime’s extreme persecution of Christians.

But the other 9 countries among the 10 worst had Muslim populations of 50 percent or greater and were cited for “Islamic extremism” as a main cause for the persecution of Christians.

“Approximately 100 million Christians are persecuted worldwide, making them one of the most persecuted religious groups in the world,” said an Open Doors statement announcing the report. “Islamic extremism is the main source of persecution in 40 of the 50 countries on the 2015 World Watch List.”

Somalia, which ranks second on the list, has a “large majority” of Sunni Muslims, according to the State Department. The CIA World Factbook list Sunni Islam as the "official" religion of the country, and the Pew Research Center estimates a 99.8 percent Muslim population.

Muslim men during prayer. (AP)

Iraq and Syria are third and fourth on the list with Muslim populations of 99 percent and 87 percent respectively, according to the CIA’s World Factbook.

“Violence against Christians by the Islamic State and other Islamic terrorist groups increased in countries like Iraq and Syria. More than 70 percent of Christians have fled Iraq since 2003, and more than 700,000 Christians have left Syria since the civil war began in 2011,” according to Open Doors.

Afghanistan, which is fifth on the persecution list, has an 80 percent Muslim majority, according to the CIA. Sudan, according to the CIA is Sunni Muslim with a "small Christian minority. The United Nations Development Programme estimates the Muslim population at 97 percent. Iran (which is 99.4 percent, according to the CIA) and Pakistan (which is 96.4 percent, according to the CIA) are seventh and eighth on the list.

A Christian church in Mosul, Iraq that was destroyed by members of the Islamic State. (AP)

The final two countries among the 10 worst for persecuting Christians each have Muslim populations of 50 percent. In Eritrea 50 percent of the population is Sunni Muslim, 30 percent is Orthodox Christian, and 13 percent is Roman Catholic, according to the State Department. Nigeria is 50 percent Muslim, 40 percent Christian, and 10 percent “indigenous beliefs,” according to the CIA.

Open Doors USA is a Christian human rights organization which has monitored Christian persecution worldwide since the 1970s. Their WWL measures “the degree of freedom a Christian has to live out his or her faith in five spheres of life—private, family, community, national and church life, plus a sixth category measuring the degree of violence.” This year’s WWL was independently audited by the International Institute of Religious Freedom (IIRF).

"Christian persecution," says Open Doors, "is any hostility experienced from the world as a result of one's identification as a Christian. Beatings, physical torture, confinement, isolation, rape, severe punishment, imprisonment, slavery, discrimination in education and employment, and even death are just a few examples of the persecution they experience on a daily basis."

Islamic countries have always featured strongly at the top of the annual Open Doors list, but the number has increased over the past decade.

On the 2004 list four of the top ten countries were Islamic. The number rose to five in 2005 and 2006, to six in 2007 and 2008, to seven in 2009, to eight in 2010 and 2011, to nine in 2012, to eight in 2013, back to nine in 2014, and again nine this year.