A senior Jordanian official has accused the country’s former crown prince of conspiring with foreign elements in a “malicious plot” that threatened national security.

Foreign minister Ayman Safadi told reporters that the plot had been foiled at the “zero hour”.

“Then it was clear they moved from design and planning into action,” Mr Safadi said. He says some 14 to 16 people are under arrest.

Mr Safadi spoke a day after Prince Hamzah, a half brother of King Abdullah II, was placed under house arrest, in a rare public clash between top members of the long-ruling family.

The unprecedented incident has raised concerns about stability in a country seen as a key Western ally in a volatile region and drawn an outpouring of support for Abdullah.

In a videotaped statement from house arrest, Hamzah accused the country’s leadership of corruption and incompetence.

Mr Safadi, who also holds the title of deputy prime minister, said intelligence agents had been observing the plotters for some time and raised their concerns with the king.

He said Hamzah was asked to “stop all these activities and movements that threaten Jordan and its stability,” but he refused.

Mr Safadi did not identify the foreign countries allegedly involved in the plot. But he said a long-time senior official who has business ties in several Gulf Arab states, Bassem Awadallah, was involved and had been planning on leaving the country.

The US, Saudi Arabia and Arab countries across the Middle East issued strong statements in favour of Abdullah.

The swift show of support underscored Jordan’s strategic importance as an island of relative stability in the turbulent region. While the harsh criticism from a popular member of the ruling family could lend support to growing complaints about the kingdom’s poor governance, the king’s tough reaction also illustrated the limits to which he will accept public dissent.

Early on Sunday, Hamzah’s mother, Queen Noor, expressed sympathy for “innocent victims”.

“Praying that truth and justice will prevail for all the innocent victims of this wicked slander. God bless and keep them safe,” she tweeted.

In his video, Hamzah said he was visited early on Saturday by the kingdom’s military chief and told he could not go out, communicate with people or meet with them. He said his phone and internet service were cut and his satellite internet, used to record the message, was being cut off as well.

He said he was told he was being punished for taking part in meetings in which the king had been criticised, though he said he was not accused of joining in the criticism.

Hamzah then lashed out at the “ruling system” without mentioning the king by name, saying it had decided “that its personal interests, that its financial interests, that its corruption is more important than the lives and dignity and futures of the 10 million people that live here”.

He said: “I’m not part of any conspiracy or nefarious organisation or foreign-backed group, as is always the claim here for anyone who speaks out. There are members of this family who still love this country, who care for (its people) and will put them above all else.”

“Apparently, that is a crime worthy of isolation, threats and now being cut off,” he added.

Hamzah is a former crown prince who was stripped of that title by Abdullah in 2004, five years after becoming king following the death of their father, the late King Hussein.

Hamzah is a popular figure in Jordan, widely seen as pious and modest. It is extremely rare for senior members of the ruling family to clash so publicly.