A senior Jordanian official has claimed authorities foiled a “malicious plot” at the “zero hour”, as a new round of arrests reached the closest aide to Prince Hamzah, the royal alleged to have unsuccessfully conspired to oust his half-brother, King Abdullah, in a weekend coup.

The foreign minister and deputy prime minister, Ayman Safadi, said on Sunday that the country’s intelligence services had intercepted a plot as it was about to be carried out. He offered scant details but said Hamzah had liaised with a foreign government to destabilise the kingdom.

He also alleged that a foreign spy service had contacted Hamzah’s wife about leaving the country by plane, and that all communications had been monitored. Safadi said about 15 people had been arrested. The latest was Hamzah’s office director, Yasser al-Majali. Soldiers took him from his home at gunpoint, relatives said.

“Initial investigations showed these activities and movements had reached a stage that directly affected the security and stability of the country,” said Safadi. “But his majesty decided it was best to talk directly to Prince Hamzah, to deal with it within the family to prevent it from being exploited.”

Any plan to quietly contain the fallout appears to have been discarded. The allegations caught Jordan’s allies and much of the country by surprise, exposing a rare and damaging public rupture among family members and sparking highly unusual dissent from a senior royal towards a monarch who had presided over relative calm since the death of his father, King Hussein, nearly 22 years ago.

Another central figure in the alleged plot is Hassan Awadallah, a former royal court aide with close ties to King Abdullah. Speculation continues to swirl in Amman about how Hamzah and Awadallah, who were not known to have been in contact, could have emerged as co-conspirators. Hamzah is popular among the country’s military and eastern tribal leaders while Awadallah led the deregulation of the country’s private sector, a drive that created friction with many in those same communities.

Hamzah released a defiant video from under house arrest in Amman on Saturday night in which he denied any link to a coup and railed against the country’s leadership. His mother, Queen Noor, King Abdullah’s stepmother, described the allegations as a “wicked slander” and called for “truth and justice to prevail”.

The former crown prince, who was removed by King Abdullah in 2004, pointedly accused the Jordanian leadership of failures in governance and stemming corruption.

“I am not the person responsible for the breakdown in governance,” he said. “For the corruption, and for the incompetence that has been prevalent in our governing structure for the last 15 to 20 years, and has been getting worse by the year.

“I am not responsible for the lack of faith that people have in their institutions. They are responsible. Unfortunately, this country has gone from one that was at the forefront of the region in terms of education and healthcare, in terms of human dignity and freedoms, to one in which even to criticise a small aspect of a policy leads to arrest and abuse by the security services.”

The US and Israel, both long-term security partners of Jordan, rallied around King Abdullah on Sunday. “King Abdullah is a key partner of the United States and he has our full support,” said a state department spokesperson.

The Israeli defence minister, Benny Gantz, described Jordan as a “strategic ally” and said the developments were an internal matter. There was no immediate comment from Britain, which also has strong ties with Amman and is home to Abdullah’s British-born mother, Princess Muna.

Abdullah’s rein has largely been anchored by an accommodation with the country’s powerful tribes, who have given their legitimacy to the Hashemite monarchy and Jordanian royal family, which has ruled the kingdom since 1921.

The tribes’ position on the move against Hamzah is unclear, though the powerful Majali tribe released a statement on Sunday saying it was a “black day in the history of Jordan” and that its community had been subjected to “a sinful attack”.

Tribes have in the past released public statements listing their grievances with the government and calling on Hamzah to assist them. His name is also sometimes heard in supportive chants at tribal protests, but diplomats in the region said there had been no previous evidence of tribal leaders organising with the prince politically.

Apart from the powerful intelligence services, the country’s parliament and institutions have long struggled to assert their authority. The teachers’ union, the largest and most assertive in the country, was banned last year and its leaders arrested.

The alleged plot comes at a time of significant discontent among Jordanians dealing with an economy that was sluggish even before the Covid-19 pandemic decimated the country’s tourism industry. There were small but intense demonstrations last month on the 10th anniversary of the beginning of the country’s Arab spring protests.

Amman’s streets were calm on Sunday, and a regional intelligence official said the weekend arrests would not lead to a larger purge. “That’s it for now,” he said. “It was a small, tight group.”