Four senior princes including two of the most prominent members of the Saudi royal family have been detained in the Saudi capital of Riyadh, a move that could be designed to further strengthen the position of the kingdom’s de facto ruler, according to two people close to Saudi leadership.

Prince Ahmed bin Abdulaziz, an uncle of Crown Prince Mohammed bin Salman, and one of his cousins, Mohammed bin Nayef, were taken into custody Friday morning, the people said, speaking on the condition of anonymity to discuss highly sensitive internal Saudi matters.

The princes were charged with treason, a serious accusation for which they could receive the death penalty.

Mohammed bin Nayef was replaced as crown prince and heir to the throne in 2017 when King Salman elevated one of his sons, Mohammed bin Salman, to the role and gave him wide authority to effectively run the kingdom.

Mohammed bin Nayef had earlier served as the country’s interior minister, developing a close working relationship with U.S. security officials.

Both the arrested men could claim a more senior place in the line of succession to Mohammed and were seen as potential rivals to the throne.

The Saudi authorities subsequently detained two close relatives of the senior princes.

The brother of Mohammed bin Nayef, Nawaf bin Nayef, was detained on Friday in the hours following his father’s arrest. On Saturday, the son of Ahmed bin Abdulaziz, Nayef bin Ahmed, was also detained, said the person familiar with the arrests. It was unclear whether they had been taken into custody or placed under house arrest.

The two princes had returned together from a hunting trip late Thursday when they received a call summoning them to meet the crown prince at 7 a.m. Friday at the royal palace, said one of the people who had been briefed on the events by members of the royal family. When they arrived, they were taken into custody, according to the account.

The arrests come at a sensitive time for the kingdom, with oil prices plummeting and Mohammed’s decision to halt visits to Mecca in response to the coronavirus outbreak stoking discontent. The arrests were first reported by the Wall Street Journal and the New York Times.

The royal family also has faced international criticism over the October 2018 murder of Washington Post contributing columnist and Saudi critic Jamal Khashoggi. The United Nations blamed what it called an “extrajudicial execution” on Saudi state agents, and U.S. intelligence officials have privately told Congress that Mohammed, who is often called by his initials, MBS, was responsible.

The crown prince has been consolidating his power over the past couple of years, seeking to disarm critics and silence dissent at home and abroad.

While he has succeeded in concentrating authority in his own hands to a degree that’s highly unusual in the kingdom, it’s unclear what kind of opposition he might face to becoming king when his elderly father dies. It is also uncertain what may have prompted the reported detentions.

Some Saudi commentators said the arrests suggest rifts within the royal family over the succession of the crown prince, whose strong-arm tactics have alienated many princes.

“The arrest of several senior disgruntled princes such as [Ahmed] and MBN [Mohammed bin Nayef] reflects a growing discontent with the ‘Son King’ over his despicable hegemony and erratic social, economic, foreign and religious policies,” tweeted Madawi al-Rasheed, a Saudi academic based in London and a fierce critic of the crown prince.

Hugh Miles, editor of ­ArabDigest.org, a subscription service offering political analysis about the Middle East, noted that fissures within the royal family could present long-term difficulties to the crown prince once he takes the throne.

“Although many questions still remain about what has happened in Saudi Arabia in the last 24 hours, what is clear is that MBS is now facing ruling Saudi Arabia without the backing of the rest of the royal family,” said Miles, who is based in Cairo. “This is a major problem for him because any would-be Saudi King is expected not only to have the royal family’s full allegiance, but also to be able to prove it.”

As a son of the founder of the Saudi kingdom, Prince Ahmed was senior in the line of succession but was passed over in favor of a new generation of younger princes. He had been living in Britain, afraid to return after he made comments that appeared to criticize the crown prince. He returned to Saudi Arabia in 2018 following Khashoggi’s killing after being given assurances for his safety, according to the person with knowledge of the arrests.

Mohammed bin Nayef has survived four assassination attempts, including one in which he was injured by an al-Qaeda suicide bomber in 2009.

In 2017, the crown prince ordered the arrests of hundreds of princes, government ministers and business people, detaining some of them in a Ritz-Carlton hotel in the Saudi capital of Riyadh. Ostensibly an anti-corruption crackdown, the sweeps were seen as a part of his effort to consolidate power.