The International Humanist and Ethical Union (IHEU), a global organization that unites atheists, agnostics, and other religious skeptics, released a study that shows 13 Muslim countries around the world mete out execution of non-believers of Islam, according to a Reuters report.

The Freethought Report 2013 covered all 193 U.N. member states and asked the expertise of lawyers and human rights experts to look into statutes, court records and media accounts to verify the situation of atheists and non-believers.

The study found that atheists and free thinkers are always subjected to discrimination and the worst that could happen to them is execution.

"This report shows that the overwhelming majority of countries fail to respect the rights of atheists and freethinkers although they have signed U.N agreements to treat all citizens equally," Sonja Eggerickx, IHEU President, told Reuters.

IHEU's study this year is more comprehensive. It brought to the fore a full list of countries where execution, usually public beheading, takes place. The study includes Afghanistan, Iran, Malaysia, Maldives, Mauritania, Nigeria, Pakistan, Qatar, Saudi Arabia, Somalia, Sudan, United Arab Emirates and Yemen. The list of countries in the study is higher compared to seven out of 60 countries surveyed last year. The study showed that the offenses that warranted public execution are blasphemy and apostasy, or when a believer renounces the faith or switches to another religion.

The study also showed that "there are laws that deny atheists' right to exist, revoke their citizenship, restrict their right to marry, obstruct their access to public education, prevent them working for the state...."

The study asserted that when a person criticizes religious faith in these countries, his action is frequently treated as a felony that can be equated to blasphemy, which is punishable by death.

IHEU also pointed out that a more systematic oppression of atheists and non-believers take place in the European Union. In countries like Austria, Denmark, Germany, Greece, Malta and Poland, any person can be discriminated against and might face jail sentences up to three years if the person publicly expresses his non-belief.