(REUTERS) Saudi Crown Prince Nayef, a pivotal figure who supervises the daily affairs of the kingdom, is undergoing routine tests at the renowned Cleveland Clinic in Ohio, Saudi television and hospital sources said on Friday.

Saudi state television said the prince, who has been the kingdom's interior minister for decades, arrived in Cleveland for scheduled medical tests but did not release any further details.

Eileen Sheil, a spokeswoman for the Cleveland Clinic, confirmed his arrival. He is here, the Crown Prince, for routine tests.

He'll be here a few days, and then he is scheduled to go home, she added.

At about 78, Prince Nayef is part of an aging leadership in the world's top oil exporter, whose stability is key to the world economy.

King Abdullah appointed Prince Nayef to be crown prince of the major U.S. ally in October, after ex-Crown Prince Sultan died of colon cancer in New York.

Nayef, who is considered a conservative even by Saudi standards for his close ties with the austere Wahhabi sect of Islam, has been a pivotal figure and supervised the daily affairs of the kingdom in the absence of the king, who has suffered from back problems.

Saudi liberals see him as an anti-reform force who is likely to take a cautious approach to social and political change. In foreign affairs, he is expected to focus on national security, having led the kingdom's fight against al Qaeda as interior minister since 1975.

However, former diplomats to Riyadh and some analysts say he is likely to show a more pragmatic side as crown prince, and eventually as king.

Saudi state television said Nayef arrived in the United States from Morocco, where state media said on Thursday he had traveled for a private vacation.

The Cleveland Clinic is a top-ranked U.S. hospital that employs nearly 3,000 doctors and researchers.

(Additional reporting by Ellen Wulfhorst in New York, Writing by Firouz Sedarat in Dubai; Editing by Alessandra Rizzo and Philip Barbara)

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