BEIRUT — Two senior princes detained in a crackdown against potential rivals of Saudi Arabia's powerful crown prince are being held in private villas and have been allowed to call their families, according to a person with ties to the royal family.

As speculation about the motivation for the arrests swirled, the Saudi royal court sought to quell rumors that King Salman is in poor health, releasing photographs said to have been taken Sunday that show him greeting two Saudi diplomats and appearing to be well.

The detention on Friday of the king’s younger brother, Ahmed bin Abdulaziz, and one of his nephews, Mohammed bin Nayef, sparked rumors that Salman’s health might have deteriorated, prompting the bold move by Crown Prince Mohammed bin Salman, the king’s son and heir, against some of the most senior members of the royal family.

Royal guards detained the two princes as they responded to an early-morning summons to meet the crown prince at the palace, said the person with ties to the royal family, who spoke on the condition of anonymity because of the sensitivity of the subject. The princes have in the past been considered possible heirs to the crown.

The person said the princes contacted family members on Saturday and told them that they were being held not in prisons but in private royal villas. Ahmed asked relatives to send him his “bisht,” a robe worn for official engagements, prompting the person to speculate that he might soon make a public appearance, perhaps under duress.

At least two other princes — Mohammed bin Nayef’s brother Nawaf and Ahmed’s son Nayef — were also detained in what appeared to be a bid to intimidate the highest echelons of the royal family. As many as 15 senior princes might have received summonses to the palace for interrogation, according to a list of names circulating among people with connections to the Saudi court.

Rumors flew that the princes were plotting a coup, that the 84-year-old king had died or was dying. But no evidence has surfaced to substantiate them.

Another person who is close to the royal court stressed that the arrests did not signal any disruption. “It was due to an accumulation of behaviors, and the leadership lost patience with them,” he said. “There’s no transition or any drama.” The person, who also spoke on the condition of anonymity, did not specify what the behaviors were.

The arrests were consistent with Mohammed’s authoritarian style since he became the de facto ruler of Saudi Arabia in 2017, taking on most of the day-to-day running of the government from his father and embarking on a crackdown against critics and rivals.

His purges have ensnared a wide range of people: journalists; clerics; women campaigning for the right to drive; and Washington Post columnist Jamal Khashoggi, who was killed and dismembered in the Saudi Consulate in Istanbul by Saudi state agents, according to the CIA and a U.N. inquiry.

Mohammed bin Nayef served as crown prince and was in line to be the next king before Mohammed and his father ousted him in a palace coup in 2017. Ahmed, the king’s younger brother, could be seen as a more natural heir to the throne than Mohammed, because the line of succession historically passed from brother to brother among the sons of the kingdom’s founder, King Saud.

But Saudi kings have reserved the right to designate their successor by naming a crown prince. Salman anointed his son Mohammed as his heir after ousting Mohammed bin Nayef in 2017.

Locking up two princes of such senior rank “sends a message to the junior guys that ‘I can do it to the senior guys,’ so the junior guys fall into line,” said Michael Stephens of the London-based Royal United Services Institute.

There doesn’t need to be a reason for him to have done so at this time, Stephens said.

“He’s a dictator. That’s what dictators do. MBS has slowly but surely made sure people who could challenge him were removed from power and ensured that people in the family understand the message of that,” the research fellow said. “There’s not going to be much backlash, internally or externally.”

Salman has ceded most of the country’s governance and policymaking to his son. But he continues to carry out ceremonial duties and greet foreign dignitaries. He was photographed meeting British Foreign Secretary Dominic Raab a day before the arrests, and one Saudi with royal connections said the king lunched with a friend hours after the princes were detained.

Nakashima and Fahim reported from Washington.