"The secretary-general extends his profound condolences to the royal family, the government and people of Oman on the passing of His Majesty Sultan Qaboos Bin Said," said Guterres' spokesman Stephane Dujarric in a statement.

The statement highlighted the sultan's leadership, saying he "led Oman for 50 years and spearheaded the transformation of Oman into a prosperous and stable country."

"He was also committed to spreading messages of peace, understanding and coexistence in the region and globally, earning the respect of his people and those in the region and beyond," it said.

Guterres paid tribute to the sultan's "enduring contributions in the field of regional and international diplomacy," it said.