"The argument Mr Harris makes is that religion is the primary driver" of radicalism and violence, she said.

"Religion is an important part of life for the overwhelming majority of Muslims, and if it were indeed the driver for radicalisation, this would be a serious issue."

But the study, which Gallup says surveyed a sample equivalent to 90 percent of the world's Muslims, showed that widespread religiosity "does not translate into widespread support for terrorism", said Mogadeh, director of the Gallup Center for Muslim Studies.

About 93 percent of the world's 1.3 billion Muslims are moderates and only seven percent are politically radical, according to the poll, based on more than 50,000 interviews.

In majority Muslim countries, overwhelming majorities said religion was a very important part of their lives – 99 percent in Indonesia, 98 percent in Egypt, 95 percent in Pakistan.

But only seven percent of the billion Muslims surveyed – the radicals – condoned the attacks on the United States in 2001, the poll showed.

Moderate Muslims interviewed for the poll condemned the 9/11 attacks on New York and Washington because innocent lives were lost and civilians killed.

"Some actually cited religious justifications for why they were against 9/11, going as far as to quote from the Koran – for example, the verse that says taking one innocent life is like killing all humanity," she said.

Meanwhile, radical Muslims gave political, not religious, reasons for condoning the attacks, the poll showed.

The survey shows radicals to be neither more religious than their moderate counterparts, nor products of abject poverty or refugee camps.