Prince Hamza, the half-brother of Jordan's King Abdullah, says he has been placed under house arrest by Jordanian authorities and accused the country's leadership of corruption and incompetence.
Former crown prince Hamzah bin Hussein says several of his friends arrested.
Prince Hamzah was asked to "stop some movements and activities that are being used to target Jordan's security and stability", according to General Yousef Huneiti, the army chief of staff.
Hamzah's mother, American-born Queen Noor, defended her son on Twitter, referring to the ordeal as "wicked slander". King Abdullah has successfully brought political stability to the country and gained stature as a prominent Arab leader whose message has resonated especially in Western forums.
As a key United States ally, Jordan promptly received the support of the Joe Biden administration.
Under the "Abraham Accords" brokered by former U.S. president Donald Trump a year ago, four Arab countries - the United Arab Emirates, Bahrain, Morocco and Sudan - agreed to normalise ties with the Jewish state.
Yemen's internationally recognised government "affirms its absolute support and totally stands with all decisions and measures taken by His Majesty King Abdullah aimed at maintaining security and ending any attempts to destabilise the sisterly Kingdom of Jordan", state news agency Saba said.
Jordan's neighbours and allies expressed solidarity with King Abdullah over the security measures in the kingdom, an important ally of the United States.
Amid rumors of "foreign" involvement in the alleged plot, Jordan's regional neighbors were quick to voice support for the monarch.
The prince previously had meetings with a number of groups in order to "persuade them into destabilising the country", Safadi said.
These included a foreign intelligence agency contacting Prince Hamza's wife to organize a plane for the couple to leave Jordan, he said.
Domestically, Prince Hamzah's unprecedented criticism of the ruling class - without naming the king - could lend support to growing complaints about poor governance and human rights abuses in Jordan.
"We support the steps taken by King Abdullah to maintain Jordanian national security, stressing that Jordan's security and stability is a supreme Palestinian interest".
"I think King Abdullah has confirmed himself in the saddle and his son Hussein has consolidated himself as the heir to the throne", said Jawad al Anani, who served as the last royal court chief under the late King Hussein. He has good relations officially with Abdullah, his half-brother, and is a popular figure close to tribal leaders.
Abdullah had chosen Hamzah as his crown prince hours after their father died of cancer in February 1999. For the first several years he was the king's confidant and for some time the finance minister.
He had been a rising figure in Jordan, playing a key role in pushing for economic reforms in the cash-strapped country until he resigned in 2008. "As of now, there is no such indication", Oded Eran, a former Israeli ambassador to Jordan and now senior research fellow at Tel Aviv University's Institute for National Security Studies (INSS), told Israel's Army Radio.
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Jordan Begins Arrests in Possible Plot Against King
Abdullah has ruled Jordan since the 1999 death of of his father, King Hussein, who ruled the country for close to a half-century. The Gulf Cooperation Council also reaffirmed support for "all decisions and measures" taken by Abdullah.