Saudi Arabia's Crown Prince Mohammed bin Salman (MBS) has launched a sweeping crackdown targeting leading royals and security officers, according to several reports, in an apparent bid to quell potential challenges to his grip on power.

Among those detained is Prince Ahmed bin Abdulaziz, the only surviving full brother of King Salman and one of the most senior members of the ruling Al Saud family.

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Prince Mohammed bin Nayef, the king's nephew and former crown prince and interior minister, was also detained on Friday. He is believed to have been under house arrest since being replaced as crown prince by MBS, the king's son, in June 2017.

The two high-profile royals, seen as possible alternatives to MBS in succeeding the king, were reportedly accused of plotting a palace coup.

The crackdown widened over the weekend to include dozens of interior ministry officials and senior army officers, reports said, as rumours swirled on social media about King Salman's health and whether the ascension of MBS - the kingdom's de facto ruler - to the throne was imminent.

As speculation about the motives behind the detentions intensified, state media on Sunday released footage and images of King Salman greeting two diplomats and appearing to be in good condition.

There has been no official comment from Saudi authorities on the detentions.

MBS has moved to consolidate power since becoming the next in line to the throne in June 2017.

Later that year, dozens of royals, top officials and business elites were rounded up and detained at a luxury hotel in the capital, Riyadh, in what was billed as an attempt to combat corruption among the higher echelons of the kingdom's bureaucracy.