The dramatic arrests of two leading Saudi royals followed discussions between the two men about using a procedural body, led by one of them, to block the accession to the throne of the crown prince, Mohammed bin Salman, if the current monarch dies or becomes incapacitated.

Three sources have confirmed to the Guardian that the arrests of Prince Ahmed bin Abdul Aziz, the sole remaining full brother of King Salman, and the former crown prince, Mohammed bin Nayef, on Friday were ordered after details of alleged conversations were passed to the royal court.

The detention of the two men was directed by Mohammed bin Salman, whom they are accused of trying to sideline through the allegiance council, a body established in 2007 to ensure a smooth transition of power should the king or crown prince die.

The council was instrumental in securing Mohammed bin Salman as crown prince in 2017 when he won 31 out of 34 votes, ousting Mohammed bin Nayef from the line of succession and establishing himself as the country’s de facto leader, a role he has ruthlessly consolidated ever since.

Prince Ahmed is believed to have been one of the three dissenters and has remained a critic of the young crown prince. He and Mohammed bin Nayef are thought to be facing treason charges, although there were suggestions in Riyadh on Monday that such serious allegations may be watered down.

Two of the Guardian’s sources said the senior royals have been accused of trying to establish Prince Ahmed as chairman of the allegiance council, a position that is currently vacant. The move would potentially give him sway over the tribal, family and clerical discussions that would lead to the nomination of new Saudi leaders.

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The alleged discussions are not believed to have developed and appear to fall short of claims that the two men were planning a coup against the crown prince. That allegation – and the confusion that followed the arrests – shocked Riyadh, prompting speculation that the king’s health had suddenly deteriorated and his son was clearing a path to take his place.

However, King Salman was pictured receiving Saudi diplomats on Sunday, dispelling rumours of his demise, and his supporters said he had no intention of leaving his position before the G20 summit in Riyadh in November.

Western officials who have been in meetings with the 84-year-old in the past week said he was lucid and focused and appeared to have changed little over the past two years.

Two other princes, the interior minister, Abdulaziz bin Saud, and Saud al-Nayef, who were detained during the arrests on Friday, were released from detention on Sunday after being interrogated. An unknown number of other royals remain detained. Mohammed bin Salman, 33, has ruthlessly eliminated rivals from all levels of Saudi society in preparation for becoming king.

While being lauded for introducing broad cultural reforms that have given Saudi women a greater participation in society and say in their own affairs, a parallel crackdown on dissent has drawn criticism in Europe and elsewhere.

The murder and dissection of the Washington Post columnist Jamal Khashoggi in late 2018 remains a potent issue for the crown prince’s critics, many of whom claim he lacks the judgment or temperament to become leader.

“That will never go away,” said a regional intelligence official. “But it must be remembered that it plays worse abroad than it does at home. And Ahmed, or any other senior royal, would be unlikely to get traction with this. There is a widespread view now that the throne can’t be taken from him.

By convention, the allegiance council must be headed by the eldest son of the kingdom’s founder, not including the crown prince, or king. It is composed of 28 members and it is not clear whether Prince Ahmed could assume the chairman’s role.

The two senior royals are believed to be being held in villas in Riyadh. Prince Ahmed, who returned from exile in London after Khashoggi’s murder, is understood to have called his family on Saturday asking for his ceremonial robe to be delivered to him – a prerequisite to meeting other royals or appearing in public.