GENEVA (Reuters) - Atheists and other religious skeptics suffer persecution or discrimination in many parts of the world and in at least seven nations can be executed if their beliefs become known, according to a report issued on Monday.

The study, from the International Humanist and Ethical Union (IHEU), showed that "unbelievers" in Islamic countries face the most severe - sometimes brutal - treatment at the hands of the state and adherents of the official religion.

But it also points to policies in some European countries and the United States which favor the religious and their organizations and treat atheists and humanists as outsiders.

The report, "Freedom of Thought 2012", said "there are laws that deny atheists' right to exist, curtail their freedom of belief and expression, revoke their right to citizenship, restrict their right to marry."

Other laws "obstruct their access to public education, prohibit them from holding public office, prevent them from working for the state, criminalize their criticism of religion, and execute them for leaving the religion of their parents."

The report was welcomed by Heiner Bielefeldt, United Nations special rapporteur on freedom of religion or belief, who said in a brief introduction there was little awareness that atheists were covered by global human rights agreements.

The IHEU - which links over 120 humanist, atheist and secular organizations in more than 40 countries - said it was issuing the report to mark the U.N.'s Human Rights Day on Monday.

According to its survey of some 60 countries, the seven where expression of atheist views or defection from the official religion can bring capital punishment are Afghanistan, Iran, Maldives, Mauritania, Pakistan, Saudi Arabia and Sudan.

The 70-page report lists no recent cases of actual execution for "atheism" -- but researchers say the offence is often subsumed into other charges.

In a range of other countries - such as Bangladesh, Egypt, Indonesia, Kuwait and Jordan - publication of atheist or humanist views on religion are totally banned or strictly limited under laws prohibiting "blasphemy".

In many of these countries, and others like Malaysia, citizens have to register as adherents of a small number officially-recognized religions -- which normally include no more than Christianity and Judaism as well as Islam.

Atheists and humanists are thereby forced to lie to obtain their official documents without which it is impossible to go to university, receive medical treatment, travel abroad or drive.

In Europe, sub-Saharan Africa and Latin and North America, countries which identify themselves secular give privileges to or favor Christian churches in providing education and other public services, the IHEU said.

In Greece and Russia, the Orthodox Church is fiercely protected from criticism and is given pride of place on state occasions, while in Britain bishops of the Church of England have automatic seats in the upper house of parliament.

While freedom of religion and speech is protected in the United States, the report said, a social and political climate prevails "in which atheists and the non-religious are made to feel like lesser Americans, or non-Americans."

In at least seven U.S. states, constitutional provisions are in place that bar atheists from public office and one state, Arkansas, has a law that bars an atheist from testifying as a witness at a trial, the report said.

(Reported by Robert Evans)