A purge of princes and aides continued across Saudi Arabia on Saturday after the kingdom’s crown prince, Mohammed bin Salman, claimed to have foiled a coup being plotted by two of the country’s most senior royals – widely seen as among the few left standing in the way of his ascension.

Prince Ahmed bin Abdul Aziz, the only full brother of the monarch, King Salman, and Mohammed bin Nayef, who was heir to the throne until being ousted by Prince Mohammed, face treason charges after being accused of organising against the ambitious heir.

Their arrest on Friday shocked the country and sparked a new round of speculation about the 84 year old king’s hold on the throne. Exiled dissidents suggested Prince Mohammed’s announcement masked an imminent push to take power from his father. The claims were given impetus by royal court insiders, one of whom suggested through a source that the moves against the two princes were made as a preventative measure, following a sudden deterioration in the King’s health. However, those claims were firmly denied by officials inside Saudi Arabia.

King Salman, is believed to have signed the warrants that justified his brother’s arrest and that of the man slated to replace him until Prince Mohammed was drafted in, following a palace coup in 2017, and named crown prince.

Since then Prince Mohammed, now 34, has assiduously eliminated threats against him, most famously by later that year locking up much of the country’s business elite in the Ritz-Carlton in Riyadh, including senior royals, who were forced to sign over assets. Some were also stripped of their positions.

A year later, in the aftermath of the murder by Saudi agents of Jamal Khashoggi in Istanbul, Prince Ahmed was lured back to Saudi Arabia after many years living in exile in London. Known as a critic of the crown prince, his return was hailed as a sign that the hard-charging heir was prepared to tolerate dissent – a claim widely rejected by critics at home and abroad.

Prince Ahmed bin Abdul Aziz, brother to King Salman, faces treason charges. Photograph: Fayez Nureldine/AFP via Getty Images

Prince Ahmed’s status as a brother of the king, and Mohammed bin Nayef’s former role as heir, had been thought to afford them both protection. Since being ousted, Mohammed bin Nayef had been prevented from leaving the kingdom and had spent much of his time at a country property outside Riyadh. His movements and those of his former aides have been closely monitored amid an expanding crackdown on dissent across all aspects of Saudi society.

Throughout Prince Mohammed’s rise, King Salman had remained largely quiet, deferring to his son on extravagant state building projects and a cultural re-engineering that disavowed the hardline gender segregation and piety that had defined the modern Saudi state. He is known to have been at odds with Prince Mohammed over the Khashoggi murder, which the CIA believes was ordered by the crown prince, and on several appointments, but has made few decisive interventions amid the political purges.

The Saudi leader hosted the foreign secretary, Dominic Raab, in the Saudi capital on Thursday and chaired a meeting of the council of ministers two days earlier, appearing composed in both meetings. His health has been the subject of repeated rumours, but recent visitors suggest he remains engaged with most subjects.

Security forces set up roadblocks across the Saudi capital on Saturday, sparking fears of unrest in the wake of the arrests and unsubstantiated suggestions that Prince Mohammed may soon assume the throne. The king is known to be aiming to receive dignitaries for the G20 summit in Riyadh in November, a landmark event on the Saudi calendar.

“It’s difficult to be 100% about what is going on,” said a former aide to a Saudi minister. “The bubble has been so well prepared. The king is so cloistered that no one knows for sure.”

A former senior diplomat, well versed in Saudi palace intrigue, said the latest purge appeared to be part of a systematic approach to eliminating dissent as Prince Mohammed’s ascension drew near.

Using an Arabic term, “Bani”, to suggest “tribe”, he said: “So he’s gone for the Bani Abdullah, Bani Fahd and Bani Sultan. Now it’s the Bani Nayef. There’s still a son of Saud bin Nayef [Mohammed bin Nayef’s brother] at the General Intelligence Presidency. He’ll have to go, too. This is like Baghdad in the 1960s.”

In the late 60s Saddam Hussein launched a coup that purged Iraq’s monarchy and consolidated himself as leader for more than three decades.