Jordan's King Abdullah has cancelled his visit to Britain next week, the Foreign Office confirmed tonight.
It comes after thousands of protesters took to the streets in the Jordanian capital of Amman today to demonstrate about spiralling fuel costs.
The king was due to attend a series of functions next week in London and was also expected to meet Prime Minister David Cameron.
One man was killed and 75 injured in the wave of unrest across the country in recent days, which has seen protesters call for the king to be ousted.
US President Barack Obama said Crown Prince Nayef, who had been next in line to rule Saudi Arabia, the world's top oil exporter, had for decades "dedicated himself to the security of Saudi Arabia as well as security throughout the region."
Seen as a key ally for the West, Saudi Arabia has provided critical intelligence to foil al Qaeda plots, bankrolled pro-Western Arab governments and has supported Washington's attempts to isolate Iran.
Saudi Arabia's Crown Prince Nayef bin Abdulaziz al-Saud, next in line to rule the world's top oil exporter, has died just eight months after becoming heir to 89-year-old King Abdullah, the royal court said.
Analysts and former diplomats said the succession process was likely to be stable, however, with the king and a family council expected to start work on the appointment of a new crown prince, who would probably be another brother of King Abdullah.
"With deep sorrow and grief... King Abdullah mourns his brother... Crown Prince Nayef who passed to the mercy of God on Saturday outside the kingdom," said a royal court statement carried by state media.