DUBAI, United Arab Emirates (AP) — Oman’s 79-year-old ruler Sultan Qaboos bin Said is in “stable condition” and is following a doctor-prescribed medical treatment, the nation’s royal court announced Tuesday, amid days of worried speculation about his health.

A statement carried by the sultanate’s state-run Oman News Agency did not, however, explain what illness the ruler faced. Sultan Qaboos, long unmarried, has no heir and it remains unclear who will succeed him in this nation on the eastern edge of the Arabian Peninsula.

Sultan Qaboos traveled to Belgium for a week in December for what was described then as “medical checks.” He returned to Oman, but rumors soon spread that he faced a serious relapse, with social media posts praising his long rule since 1970, when he ousted his father in a bloodless coup.

Tuesday’s statement from the Diwan Court sought to ease those concerns.

“The Royal Diwan Court wishes to inform the people that the Sultan Qaboos bin Said … is following the prescribed medical treatment and that he is in a stable condition, thanks to God,” the statement said. “The sultan thanks his people all around the world for them sharing their good wishes and prayers for him.”

Sultan Qaboos previously spent eight months in Germany, returning to the sultanate in 2015 after receiving medical care. It remains unclear what ails him, though a report by the Washington Institute for Near-East Policy published early Tuesday described the sultan as a “79 year old with diabetes and a history of colon cancer.”

“For Oman, there would be no good time to lose the sultan, who has ushered his country into the modern age,” analyst Simon Henderson wrote. “With succession in the offing, the sultan’s lack of an heir from his one brief marriage and his decision to not identify a successor make for mystery and some anxiety.”

Oman under Sultan Qaboos has served as an interlocutor between Iran and the U.S. Those efforts reached their zenith with the secret talks between Iranian and American the sultanate hosted that gave birth to Tehran’s 2015 nuclear deal with world powers.