"The kingdom's stability and security transcend everything", said Ayman Safadi, Jordan's foreign minister and deputy prime minister, as he accused Hamzah and two senior Jordanian officials of conspiring with foreign elements to destabilize the kingdom.
"We are closely following the reports and in touch with Jordanian officials", State Department spokesman Ned Price said in a statement late Saturday.
Jordan's Prince Hamzah said he would defy orders limiting his freedom of movement after authorities.
He accused the prince of seeking to mobilise "clan leaders" against the government, adding that the plot had been "nipped in the bud" at the "zero hour".
"The kingdom stresses its full support for the Hashemite kingdom of Jordan. and for the decisions and measures taken by King Abdullah II and Crown Prince Hussein to safeguard security and stability", it said.
The widow of Jordan's late king defended her son, Prince Hamzah, against allegations by the authorities that he carried out actions targeting "security and stability" in the kingdom.
Prince Hamza is a former crown prince, as his half-brother King Abdullah removed him from the line of succession in 2004.
Prince Hamza's mother, Queen Noor of Jordan, said in a tweet: "Praying that truth and justice will prevail for all the innocent victims of this wicked slander. God bless and keep them safe", she said on Twitter.
He added that at least 16 people, including a former adviser to King Abdullah and another member of the royal family, had been arrested over the plot to "undermine the security" of the country. He claimed the prince recorded the conversations, passed them to foreign sources and issued his video message "in an attempt to distort facts and to gain sympathy domestically and internationally". "The Israeli security establishment would not look favorably toward any real instability in Jordan that triggers a Palestinian crisis". In 2004, however, King Abdullah II replaced Prince Hamzah and later designated his eldest son as the Crown Prince of Jordan.
Awadallah, a proponent of economic reforms, resigned as chief of the royal court in 2008 amid allegations of interference in sensitive political and economic issues.
These included a foreign intelligence agency contacting Prince Hamza's wife to organise a plane for the couple to leave Jordan, he said.
Security forces also arrested the top official and member of the royal family Sharif Hassan Ben Zaid. In a six-minute video provided to the BBC by his lawyer, he said he was "not part of any conspiracy". "When an army chief of staff says that, this is something that I think is unacceptable". The government alleges that Crown Prince Hamzah had liaised with foreign entities and that he was making plans to flee the country. "This file is now more or less closed".
Which countries backed the king?
The United States swiftly announced its "full support" for Abdullah.
Stability in Jordan and the status of the king have always been a concern throughout the region, particularly during the Trump administration, which gave unprecedented support to Israel and sought to isolate the Palestinians, including by slashing funding for Palestinian refugees.
Although the developments in Jordan have come as a surprise for many, DW reporter Aya Ibrahim says there were indications a closer look at the developments on the ground show what led to this point.
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. "It has also had to undergo some very serious austerity measures that are starting to be really painful for ordinary Jordanians", she told DW News.
A Jordanian analyst, who declined to be named, said Hamzah had recently "stepped up his criticism of what he described as corruption within the government in front of his circle of friends".
Amman-based journalist Rana Sweis told DW that Prince Hamzah's video appeal was "unprecedented".
"Jordan is normally a stable Arab kingdom that has been a staunch ally of countries in Europe and the U.S., particularly when it comes to counterterrorism cooperation in the Middle East", Sweis said. It is bordered by Israel, Syria, Iraq and Saudi Arabia.