Non-Muslims in Saudi Arabia are free to practise their religion in the ultra-conservative Gulf kingdom but must do so in private, the head of a government watchdog told AFP on Monday.

"This matter is well known and doesn't require reasserting -- non-Muslims can conduct their religious ceremonies in secret but not in public," said the head of the Saudi Human Rights Commission, Turki al-Sudairy.

International human rights groups say Saudi Arabia, which applies a strict interpretation of Sunni Islam, does not tolerate religious practices by non-Muslims.

Sudairy stressed that allowing non-Muslims to openly practise their faith would conflict with the "religious politics of the kingdom" and "cause a number of problems, the most serious being preaching... in the cradle of Islam".

New York-based Human Rights Watch in January accused Saudi Arabia, the birthplace of Islam, of carrying out a wave of arrests and deportations against mainly south Asian followers of the Ahmadi faith that it said amounted to a "grave violation" of religious freedom.

It said the Saudi authorities had arrested 56 non-Saudi followers of the faith, "including infants and young children" and deported at least eight to India or Pakistan.

Ahmadis consider themselves Muslims and follow the teachings of Mirza Ghulam Ahmad, a 19th-century Indian Muslim scholar. In Saudi Arabia, the faith is practised by a small minority of foreign workers, primarily from India and Pakistan.

But many Muslims view the Ahmadis as heretics because of the elevated status they afford to the faith's founder. They also face persecution in Pakistan and Bangladesh.

Human rights organisations say the Saudi government also discriminates against Shiite Muslims, who are estimated to make up at least 10 percent of the citizen population of some 17 million.

Saudi Arabia is dominated by the austere Sunni doctrine of Wahabism, many of whose followers deride Shiite Muslims as rejectionists.