Saudi Arabia's Crown Prince Nayef has left the kingdom for a holiday and medical tests, the state news agency reported on Saturday, in a country where the health of senior royals is keenly watched.
"Crown Prince Nayef ... went abroad for a personal vacation during which some medical tests have been scheduled," Saudi Press Agency reported.
Nayef, who is 77 or 78, has been interior minister since 1975 and was made King Abdullah's heir apparent in October after the death of the former crown prince, Sultan.
He returned to Saudi Arabia in April after spending a month abroad following medical tests in Cleveland, in the United States. The nature of the tests has not been revealed.
In the world's top oil exporter political power is held almost exclusively by the top-ranking members of the al-Saud ruling family, meaning the health of senior royals is closely scrutinised.
After the death of the kingdom's founder, Abdulaziz ibn Saud, power has been passed down between some of his nearly 40 sons who lived to adulthood.
King Abdullah, who is nearly 90, had a back operation last year.
He is the fifth of Ibn Saud's sons to become king and nearly 20 remain alive, although only a few of these are thought likely candidates to rule the U.S. ally.
Although Nayef has a reputation as a conservative who is averse to the cautious social changes being pushed by his elder brother, analysts have speculated he might prove less resistant to reform as king.
The presumed next in line after King Abdullah and Crown Prince Nayef is Prince Salman, another brother who was promoted to the role of defence minister in November after spending five decades as Riyadh governor.
Short link: