WASHINGTON ? The world's 1.57 billion Muslims make up nearly a quarter of the global population, with most of them clustered in countries in Asia, a study published Thursday showed.

Nearly two-thirds of the world's Muslims live in Asia, with only one in five in the Middle East and North Africa -- even though more than half of the 20 countries in that region are overwhelmingly Muslim, the study by the Pew Forum on Religion and Public Life found.

Indonesia has the largest number of Muslims of any country -- nearly 203 million, which represents just under 13 percent of the global total. Indonesia's Muslims make up around 88 percent of the country's population.

Other countries in the top five in terms of numbers of Muslims are Pakistan, where there are 174 million Muslims who make up around 96 percent of the country's population, followed by India with around 161 million Muslims who represent just 13.4 percent of the population.

The overwhelming majority of Muslims are Sunnis -- between 87 and 90 percent versus 10-13 percent who are Shia Muslims.

The report estimates there are between 154 million and 200 million Shia Muslims in the world; around 70 million of them live in Iran.

Egypt has the largest Muslim population in the Middle East and northern Africa region, while Nigeria has the largest Muslim population in sub-Saharan Africa.

Both countries have around 78 million Muslims, but in Egypt they are in a clear majority -- nearly 95 percent -- while in Nigeria, which is Africa's most populous nation, they make up around half the population.

Europe has around 38 million Muslims, around 16 million of whom live in Russia, four million in Germany and 3.5 million in France.

Of the approximately 4.6 million Muslims in the Americas, more than half, or about 2.5 million, live in the United States.

Data from 232 countries and territories were gathered and analyzed for the study, which the Pew Forum called "the largest project of its kind to date."