OMAN, Jan. 11 (CGTN) -- Oman's Sultan Qaboos bin Said passed away on Friday evening, state media said early Saturday, announcing three days of national mourning.

"The Diwan of Royal Court announces mourning and disrupts the official work of the public and private sectors for 3 days and flags at half-mast in the next forty days," the state TV public channel said on Twitter.

The sultan, the Arab world's longest-serving ruler, who ruled Oman for almost half a century, died at the age of 79. The cause of his death has not been disclosed.

He deposed his father in a bloodless coup with the support of Britain, Oman's former colonial power, in 1970. Using its oil wealth, he then set Oman on a path to development.

Oman state news agency ONA said Qaboos died after "a wise and triumphant march rich with generosity that embraced Oman and extended to the Arab, Muslim and entire world and achieved a balanced policy that the whole world respected."

Qaboos had been unwell for years and had spent a week in Belgium undergoing medical treatment in early December.

No heir apparent

Qaboos had no children and had not publicly appointed a successor.

A 1996 statute says the ruling family will choose a successor within three days of the throne becoming vacant. If they fail to agree, a council of military and security officials, supreme court chiefs and heads of the two consultative assemblies will put in power the person whose name has been secretly written by the sultan in a sealed letter.

The new sultan should be a member of the royal family, as well as "Muslim, mature, rational and the legitimate son of Omani Muslim parents."

Local experts say more than 80 men meet the criteria, but one name stands out: Asad bin Tariq.

Tariq, 65, had been appointed deputy prime minister for international relations and cooperation affairs in 2017.

The move was seen as a clear message of support for the sultan's cousin and "special representative" since 2002.