Saudi king's son Mohammed bin Salman is new crown prince

Prince Mohammed bin Salman (left) replaces prince Mohammed bin Nayef (right) as crown prince

Saudi Arabia's king has appointed his son Mohammed bin Salman as crown prince - replacing his nephew, Mohammed bin Nayef, as first in line to the throne.

King Salman's decree also means Prince Mohammed bin Salman, 31, will become deputy prime minister while continuing as defence minister.

Prince Mohammed bin Nayef, 57, has also been removed from his role as head of domestic security, state media say.

He has pledged allegiance to the new crown prince, news agency SPA reports.

King Salman, 81, acceded to the throne in January 2015 after the death of his half-brother Abdullah bin Abdul Aziz.

He announced his first major cabinet reshuffle a few months later, appointing Prince Mohammed bin Nayef as crown prince and Prince Mohammed bin Salman as deputy crown prince.

That was described as a break with tradition as Saudi Arabia has previously been ruled by kings in their 70s or 80s.

Prince Mohammed bin Salman's latest promotion, and his rapid ascent, is seen by the younger generation as a sign that things are changing.

As defence minister and deputy crown prince, he has led Saudi Arabia's war in Yemen, and overseen the kingdom's energy policy.

Prince Mohammed bin Nayef was the kingdom's security chief for many years and was known for his strong stance against jihadist militants.

He had headed up the counter terrorism portfolio, and had good relations with Saudi Arabia's Western allies, including the US and UK.