By Andrew Torchia

DUBAI - Oman is replacing the executive president of its central bank after he held the post for 26 years, the official ONA news agency reported on Tuesday, quoting a royal decree by the Gulf nation's ruler Sultan Qaboos.

Hamood Sangour al-Zadjali had run the central bank since 1991, overseeing an economic boom fuelled by oil and gas exports and then, in the last few years, managing pressure on the economy caused by a plunge in energy prices.

He was the region's longest-serving central bank chief.

He is being replaced by Tahir Salim al-Amri, a former director-general of treasury and accounts at the Ministry of Finance, ONA said.

At the ministry, Amri headed the committee which arranged the government's first sale of Islamic bonds in 2015, a 250 million rial ($650 million) issue. More recently, he was deputy chief executive of Oman Finance & Investment Co.

ONA did not say why Zadjali, who is about 70, was being replaced. Contacted by telephone, Zadjali declined to comment on the reasons for his departure or on whether central bank policy might change, saying merely that government officials were royal servants who served at the sultan's pleasure.

If oil and gas prices stay low, keeping government finances in deficit, one of Amri's challenges in coming years may be to maintain investor confidence in Oman's currency and banking system.

Credit rating agency Moody's lowered its outlook for the Omani banking system on Monday to negative from stable, saying low oil prices were weighing on economic growth and reducing the government's capacity to support the banks if needed.

ONA also said on Tuesday that Sultan Qaboos had made changes to the central bank's board of governors, appointing Sultan bin Salim bin Said al-Habsi as deputy chairman of the board for a five-year term. It did not give reasons for the changes.

(Reporting by Andrew Torchia; Editing by Hugh Lawson and Edmund Blair) ((andrew.torchia@thomsonreuters.com; +9715 6681 7277; Reuters Messaging: andrew.torchia.thomsonreuters.com@reuters.net))