Media has been stating that for medical treatment for a back ailment complicated by a blood clot, King Abdullah of Saudi Arabia will leave for the United States on Monday and Crown Prince Sultan is returning from a vacation.

Western diplomats in Riyadh, the Saudi capital, said that Saudi Arabia, which has no political parties or elected parliament, is preventing a power vacuum and reassure Washington and other allies as the prince returns from Morocco where he has been since August.

The kingdom's political stability is getting global attention. More than a fifth of the world's crude oil reserves are controlled by Saudi Arabia controls, a major holder of dollar assets and home to the biggest Arab bourse and is a vital United States ally in the region.

At the helm of a pivotal Muslim country, the king, who is 86, is valued by Washington as a moderate. After a blood clot complicated a slipped disk he suffered the previous week, on Friday he entered a hospital.

Sources said, "The king will leave on Monday for the United States to complete medical tests."

To assure the public that the king was healthy and would return to lead the country, Saudi's health minister, Dr. Abdullah al-Rabeeah, appeared on state television.