Oman has moved quickly to fill a leadership gap following the death of long-reigning Sultan Qaboos bin Said whose pursuit of a strict neutral foreign policy ensured friendly relations with all the neighbouring countries in the often volatile Persian Gulf region.

His cousin, Haitham bin Tariq al Said, who has assumed the reins of power, pledged to continue Qaboos' legacy.

The former culture minister was sworn in before the ruling family council on Saturday morning, just hours after the announcement of Sultan Qaboos' death.

State television said authorities had opened a letter by Sultan Qaboos naming his successor, without elaborating, before announcing Haitham bin Tariq as the new ruler.

Qaboos, in power since 1970, died on Friday, raising fears of a leadership crisis since he had no children. Qaboos was instrumental in ensuring stability in Oman, the largest regional non-Opec oil exporter with a daily production capacity of about 1 million barrels of oil equivalent.

Qaboos is credited with transforming Oman from a backwater threatened by a secessionist movement in the south to a modern and wealthy state.

He carved the role of an international mediator for Oman, mediating between the US and Iran and keeping out of regional conflicts such as the Saudi-led boycott of Qatar.

His death comes at a time of rising tensions between the US and Iran.

In his first address to the nation, Sultan Haitham bin Tariq pledged to maintain the Gulf state's neutral foreign policy, which he said was built on peaceful coexistence and maintaining friendly ties with all nations.

"We will continue to follow in the same course the late sultan adopted … embracing foreign policies based on peaceful coexistence among peoples and countries without any interference in the domestic affairs of other states.

"We will continue as always … contributing and calling for peaceful and amicable solutions for all disputes," he added, paying tribute to the late sultan.

"The least we hope for is to follow in his [Qaboos] footsteps and remain guided by his wisdom into the future, and preserve … the achievements he made," Sultan Haitham bin Tariq said.