Jordan said it uncovered a plot to destabilize the kingdom that involved King Abdullah II's half-brother and extended beyond the country's borders.

The sibling, former Crown Prince Hamza Bin Hussein, worked in concert with foreign entities, Deputy Prime Minister Ayman Safadi said on Sunday, in a first official explanation of a string of arrests a day earlier. More than 16 people, including at least one other royal, were taken into custody, he said at a news conference in the capital, Amman.

"There was an effort to target Jordan's security and stability, this effort was foiled," he said, giving no evidence to back up his claims. He declined to say whether the unidentified foreign entities were people or governments, and if any money was paid to those involved in the alleged plot.

The crackdown comes as Jordan struggles with a worsening squeeze on its finances and a resurgence of Covid-19 cases that has prompted the government to renew restrictions on movement. The U.S. most recently provided the Middle East kingdom with $700 million in August.

"We are closely following the reports and in touch with Jordanian officials," State Department spokesman Ned Price said in a statement late Saturday. "King Abdullah is a key partner of the United States, and he has our full support."

Jordan's stability is crucial to the region as it sits at the crossroads of the Israeli-Palestinian conflict. It's home to as many as 2 million Palestinian refugees and their descendants, and chaos there could endanger the security of Israel, with which it shares a frontier and made peace in 1994. Bordering both Syria and Iraq, the kingdom has also fashioned itself as a force for moderation in a turbulent neighborhood.

Security personnel and armored vehicles were seen parked outside royal palaces and patrolling the Dabouq neighborhood of the capital, Amman, on Saturday. The Washington Post said earlier that Hamza, the eldest son of the late King Hussein and his fourth wife Queen Noor, was under house arrest at his palace in Amman. It cited a senior Middle East intelligence official briefed on the events as saying there was an ongoing investigation into an alleged plot to unseat King Abdullah, Hamza's older half-brother.

Hamza was the crown prince for four years before the title was transferred in 2004 to the current king's eldest son, Hussein. He has occupied various roles, including brigadier in the Jordanian army. In a six-minute video provided to the BBC by his lawyer, he said he was "not part of any conspiracy."

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"I had a visit from chief of general staff of the Jordanian armed forces this morning in which he informed me that I was not allowed to go out, to communicate with people or to meet with them because in the meetings that I had been present in -- or on social media relating to visits that I had made -- there had been criticism of the government or the king," Hamza said in the video. He added that his Internet and phone lines had been cut.

On Twitter, Hamza's mother, Queen Noor called the incidents a "wicked slander".

Chairman of the Joint Chiefs of Staff Major General Yousef Huneiti on Saturday denied claims about the arrest of Hamza and said the prince was merely asked to stop "movements and activities that are used to target" the security and stability of Jordan. He added that the move was part of joint investigations undertaken by security agencies, as a result of which Hasan Bin Zeid, a member of the royal family, along with several others, including Bassem Awadallah, a former cabinet minister, were arrested.

The army chief indicated that the investigations were ongoing and their results will be announced "with full transparency and clarity."

Awadallah, who holds a doctorate from the London School of Economics and Political Science, has served in various positions in Jordan, including economic secretary to the prime minister, minister of finance and head of the royal court. Until 2018, he was King Abdullah's personal envoy to Saudi Arabia, where he was close to Crown Prince Mohammad bin Salman.

Saudi Arabia, the United Arab Emirates, Qatar, Egypt and other Arab states joined the U.S. in expressing support for King Abdullah.

Saudi King Salman bin Abdulaziz called Jordan's King Abdullah II, and Crown Prince Mohammed bin Salman spoke with both the king and with Jordan's Crown Prince Hussein bin Abdullah, according to the SPA news agency.

"The Kingdom stands and its full solidarity with the sisterly Hashemite Kingdom of Jordan and the Kingdom's support for all the measures that His Majesty takes to preserve the security of Jordan and maintain its stability," King Salman was quoted as saying.

"The Biden administration would view the potential of a failed state as detrimental to regional stability," said Ayham Kamel, the New York-based head of Eurasia Group's Middle East and Africa research team. "The Israeli security establishment would not look favorably toward any real instability in Jordan that triggers a Palestinian crisis."