Muscat, Oman - Foreign officials have arrived in Oman's capital, Muscat, to offer condolences to Sultan Haitham bin Tariq Al Said, the successor to the late Sultan Qaboos who died on Friday after nearly 50 years at the throne.

Haitham acceded to power on Saturday after being named by Qaboos in a letter that was opened in the presence of members of the royal family and security services.

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Three days of national mourning were declared upon Qaboos's death at 79, and condolences are currently being accepted at the Al Alam Palace, a ceremonial location in Muscat used to welcome dignitaries.

Among the first to pay their respects on Sunday were Iranian Foreign Affairs Minister Mohammed Javad Zarif, on behalf of Iran's President Hassan Rouhani, and the emir of Qatar, Sheikh Tamim bin Hamad Al Thani.

Oman has maintained close relations with both nations despite other Gulf countries seeking to push back against the influence of Tehran and Doha in the region.

On Saturday, Zarif tweeted in Arabic that Qaboos's death was "a loss for the region".

Under Qaboos, Oman became a centre for back-door negations between Iran and the United States as well as between representatives of Yemen's Houthi rebels and Saudi Arabia, who have been locked in a devastating conflict since 2015.

Sultan Haitham has been welcoming officials from across regional and global divides in a show of the success of his predecessor's forcing policy, defined as being "an enemy to no one and a friend to all".

These well-wishers included Abu Dhabi Crown Prince Mohammed bin Zayed al-Nahyan, Kuwaiti Emir Sabah Al Ahmad Al Jaber Al Sabah, Yemeni President Abd-Rabbu Mansour Hadi, Tunisian President Kais Saied and former French President Nicolas Sarkozy.

Haitham also welcomed an envoy of Ugandan President Yoweri Museveni, Oyo Nyimba Kabamba, who is the king of Tooro, one of the five traditional kingdoms of Uganda.

Omani state media was not covering the condolences live on Sunday and issued the same few lines on each meeting: Officials had offered their sincere condolences and sympathy on the death of Qaboos, calling on God to have mercy on his soul. They also wished "patience and solace" to the new sultan, the royal family and the Omani people.

Queen Elizabeth: Qaboos was 'a good friend'

Sultan Haitham also welcomed the United Kingdom's Prince Charles and the country's defence secretary, Ben Wallace, as well as the chief of staff of the British army, General Nicolas Carter.

Oman state media earlier in the day said the sultan had received a cable of condolences from Britain's Queen Elizabeth II, who said in a statement on Saturday that Sultan Qaboos was a "good friend" and that she was "deeply saddened" by his death.

Queen Elizabeth had visited Oman in 2010 and said it remained a "cherished memory".

Oman has long enjoyed close ties with the UK, dating back to Qaboos's accession to power in 1970 in a bloodless coup against his father that was heavily backed by the UK.

"His devotion to Oman, to its development and to the care of his people was an inspiration," Queen Elizabeth said.

"He will be remembered for his wise leadership and his commitment to peace and understanding between nations and between faiths."

Trump: Qaboos 'friend to all'

While no US envoy had arrived in Muscat to pay condolences as of Sunday afternoon, US President Donald Trump said in a statement that Sultan Qaboos had undertaken "unprecedented efforts to engage in dialogue and achieve peace in the region.

He also said Qaboos had been a "friend to all" and a "true partner and friend to the United States, working with nine different American presidents."

Oman has long been a partner of the US, including in military cooperation through an agreement that has allowed the US to use Omani bases.

"Sultan Qaboos will truly be missed. Let us take comfort in knowing that his powerful legacy will live on," the statement said.