Sultan Qaboos, the longest-reigning leader of the modern Arab world, has died at the age of 79, the royal court said on Saturday.

“With great sorrow and deep sadness [...] the royal court mourns His Majesty Sultan Qaboos bin Said, who passed away on Friday,” the court said in a statement.

His cousin Haitham bin Tariq, Oman's culture minister, was named as Qaboos' successor, the government said on Saturday.

"Haitham bin Tariq was sworn in as the new sultan of the country [...] after a meeting of the family which decided to appoint the one who was chosen by the sultan," the Oman government said in a tweet. Discussions over the late ruler's successor were held as he had left no apparent heir. He was unmarried and had no children or brothers.

Qaboos, who ruled Oman since 1970 when he deposed his father in a palace coup, had been ill for some time and had been believed to be suffering from colon cancer.

Prime Minister Imran Khan, in a tweet, offered his condolences on the death of Qaboos and termed the ruler as a "visionary" who "transformed Oman into a vibrant, modern state".

"Oman has lost a beloved leader and Pakistan a close, trusted friend. May his soul rest in eternal peace," the premier said.

PML-N President and Leader of the Opposition in the National Assembly Shehbaz Sharif also extended his condolences to the people of Oman and said that Qaboos' services for the development and progress of his country will be remembered.

The matter of succession

According to the Omani constitution, the royal family shall, within three days of the throne falling vacant, determine the successor.

Had the royal family failed to agree on a name, the person chosen by Qaboos in a letter addressed to the royal family would be the successor. The government's statement, which announced the new sultan, implies that Qaboos had named Haitham.

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

Haitham, 65, was being named as a potential successor along with Shihab bin Tariq, 63, who was a close adviser to the sultan and Asad bin Tariq, 65. Asad had been appointed deputy prime minister for international relations and cooperation affairs in 2017. The move was seen as a clear message of support to the sultan's cousin and "special representative" since 2002.

Discreet mediator

Qaboos transformed the Arabian Peninsula nation from a backwater into a modern state while pursuing a moderate but active foreign policy.

Having played a role in Iran's nuclear deal with world powers while preserving its membership in the Saudi-led Gulf Cooperation Council, Oman has emerged as the Gulf's discreet mediator.

The sultan's death comes amid increased tensions between Tehran and Washington, who on Friday piled new sanctions on the Islamic republic following the killing of a top Iranian leader in Iraq.

The sanctions marked the latest salvo in a US-Iranian confrontation that risked sliding into war a week ago with the deadly US drone attack on general Qasem Soleimani, by some measures the second most influential person in Iran.

Unlike other Arab states, Qaboos did not contest Egypt's 1979 peace treaty with Israel, opening a trade office in Tel Aviv in the mid-1990s — shuttered in 2000 during a Palestinian uprising.

In October 2018, Israeli Prime Minister Benjamin Netanyahu held surprise talks with Qaboos in Muscat.

It remains to be seen whether the next Omani ruler will take the same moderate approach in a region often in turmoil.

With additional input from Javed Hussain.