Jordan's King Abdullah II said Thursday his half-brother Prince Hamzah, accused of involvement in a coup plot last year, is in a state of "delusion" and will remain under house arrest.

Authorities in Jordan announced in April last year that they had foiled a bid to destabilise the Western-allied kingdom, marking a rare crisis in a nation seen as a pillar of regional stability.

Two former officials were sentenced to 15 years in jail in July after they were found guilty of conspiring to topple the king. Prince Hamzah escaped prosecution but was ordered into house arrest.

The king said in a statement released on Thursday that his half-brother would remain under house arrest, and that further restrictions would be imposed upon him.

"A Royal Decree was issued, approving the recommendation of the council formed in accordance with the Royal Family Law, to restrict the communications, place of residence, and movement of Prince Hamzah," the statement from the royal palace said.

Prince Hamzah is seen delivering a speech in 2009
Prince Hamzah is seen delivering a speech in 2009 AFP / Attila KISBENEDEK

"We will provide Hamzah with all that he requires to live a comfortable life, but he will not have the space he once abused to offend the nation, its institutions, and his family, nor to undermine Jordan's stability," Abdullah II said, in a letter to the Jordanian people.

"I will never allow our country to be held hostage to the whims of someone who has done nothing to serve his country," he added.

Hamzah, 42, had in April announced he was "renouncing the title of prince", a month after a royal court statement said he had apologised to the king for "his actions and offences".

But Abdullah II said on Thursday that Hamzah had during the past year or so "exhausted all opportunities to restore himself on the right path".

Prince Hamzah, seen in this file photo taken on April 17, 2012 in the Wadi Rum desert
Prince Hamzah, seen in this file photo taken on April 17, 2012 in the Wadi Rum desert AFP / KHALIL MAZRAAWI

"The delusion he lives in is not new," the king said.

"Not long after vowing to renounce his erroneous ways, he goes back on his promises and returns to the path he chose years ago, putting his interests before the nation."

The king appointed Hamzah as crown prince in 1999, at the request of his late father, King Hussein, but removed him from the post in 2004, later naming his son, Prince Hussein, as next in line to the Hashemite throne.

"Over the past years, I have exercised the highest degrees of tolerance, self-restraint, and patience with my brother... and have been disappointed time and again," the king added.

Hamzah's mother, American-born Queen Noor, said on Twitter shortly after the king's announcement that "some truly bizarre and stranger than fiction stuff (is) circulating right now," without elaborating.

The two officials convicted last year were former royal court chief Bassem Awadallah and an ex-envoy to neighbouring Saudi Arabia, Sharif Hassan bin Zaid.

Both were reported to have had close ties to Riyadh, and were found guilty of "incitement against the ruling system" and "acts that could threaten society and create sedition".

Hamzah was not charged in the trial, but the charge sheet said he was "determined to fulfil his personal ambition to rule, in violation of the Hashemite constitution and customs".

In April last year, in a video message posted online, Hamzah accused Jordan's rulers of corruption and ineptitude.

On Thursday, the royal palace said they would "not be surprised" if Hamzah were to release other messages.

"I, and our people, will not waste time responding to him," Abdullah II said. "I am convinced he will continue to spread this false narrative, but we do not have the luxury of time to deal with it."