North Korea, Iran and Saudi Arabia are the worst persecutors of Christians around the world, according to a ranking released Wednesday by a Christian mission agency. In an annual assessment of the 50 worst state persecutors of Christians by California-based Open Doors USA, North Korea topped the list for the seventh year in a row. Iran moved up to the second position on Open Doors' World Watch List, bumping Saudi Arabia down from last year, to the third slot. "Maryam Rustampoor and Marzieh Amirzadeh were arrested simply for being Christians and refusing to recant their faith in Jesus Christ," said Carl Moeller, president and CEO of Open Doors USA. Although they've been released, he said, "Hundreds of other believers still remain at risk inside Iran." The rankings, based on a 53-question survey of Open Doors contacts, field workers and church leaders, focus on legal restrictions, attitudes and incidents of persecutions. This year, Somalia moved up to No. 4, from No. 5, because in April the parliament voted unanimously to institute Islamic law. Other countries in the top 10 include Afghanistan, Yemen, Mauritania, Laos and Uzbekistan. Open Doors USA noted that eight of the 10 worst persecutors have Islam as their dominant religion, while two - North Korea and Laos - are communist countries. Out of 50 countries on the list, 35 have Islamic governments. Moeller said it was no surprise that North Korea topped the list. "There is no other country in the world where Christians are persecuted in such a horrible and systematic manner," he said, noting that three generations of a family are often imprisoned when one relative is incarcerated. According to the World Watch List report released Wednesday: "The North Korean regime especially targeted secret Christians all over North Korea to arrest and kill them. They have arrested and tortured Christians in various horrible ways, such as sometimes using them as a means of testing biological or chemical weapons." In Iran, where protestors have clashed with government officials for months following the contested re-election of President Mahmoud Ahmadinejad, Open Doors said a wave of arrests of Christians that began in 2008 grew stronger in 2009, resulting in 85 arrests. Speculating that the arrests were meant to distract attention from internal problems, the report noted: "Under the judicial interpretations of Sharia law, any Muslim who leaves Islam to embrace another religion faces the death penalty" in Iran, and many churches are monitored by secret police. Other changes to the list include Mauritania jumping to the top 10 for the first time. Open Doors said it moved up 10 spots because of the murder of a Christian aid worker in June; the arrest and torture of 35 Christians in July, and the arrest of 150 sub-Saharan Christians in August. Tahe list included the Palestinian Authority and Gaza, at No. 46, below Egypt at 20 and Libya at 22. Syria was ranked 41, Jordan 39 and Cuba came in at 38. Israel did not make the list of 50.