Saudi Arabia's Crown Prince Mohammed bin Salman had plotted to oust his rival before being eventually appointed as the first in line to the throne, according to reports.

Salman, son of the Saudi King, was appointed as Crown Prince and deputy prime minister, replacing his cousin Mohammed bin Nayef as first in line to the throne on 21 June. The new appointment came as a series of decrees amended Article V of the Kingdom's statute of ruling.

Unnamed sources close to the Saudi family and US officials have now claimed the appointment was not as smooth as it was previously believed and Salman's alleged plot to oust Nayef had spread concern among counter-terrorism officials in the US, the New York Times reported.

It is believed Nayef had been pressurised to step down as the Kingdom's Crown Prince. The night before Salman's appointment, a group of security officials and senior princes including Nayef gathered at the Safa Palace in Mecca after being informed that King Salman wanted to see them, sources claimed.

Nayef was allegedly taken into another room, where royal court officials took his phones and pressurised him to step down as crown prince and interior minister, sources further claimed.

It is believed Nayef refused at first, but eventually gave in and returned to his palace in the city of Jidda, where he was barred from leaving. The next day, he was officially replaced by Salman.

Sources claimed Nayef had been deemed as unfit to be the country's new king due to concern he might have developed an addiction to medications he started taking following an assassination attempt in 2009.

One American official and one adviser to a Saudi royal also claimed Nayef had opposed a possible embargo targeting Qatar, which Riyadh accuses of supporting terrorism and implementing policies that destabilises the geopolitical equilibrum of the Gulf.

A written statement by a senior Saudi official denied the claims and said the Allegiance Council, a body of senior princes, had approved the new appointment in "the best interest of the nation."

Salman's appointment was endorsed by 31 out of 34 members of the Allegiance Council, composed of senior members of the ruling Al Saud family.

After being deposed, Nayef pledged allegiance to Salman and said "I am content." In response, Salman said: "We will not give up taking your guidance and advice."

Bin Salman
Saudi Arabia's Crown Prince Mohammed bin Salman Reuters/Charles Platiau