Saudi Arabia's powerful Crown Prince Mohammed bin Salman has asked a US federal court to throw out a lawsuit which accused him of trying to have an ex-intelligence official assassinated.

Prince Mohammed's lawyer told the federal court in Washington that Saad Aljabri's suit filed in August did not provide evidence of the "hit squad" that he alleged the prince sent to kill him.

The filing Monday also said that, as designated heir to the Saudi throne, Prince Mohammed was protected by laws of sovereign immunity.

"This court lacks personal jurisdiction over the Crown Prince," it said.

"The complaint alleges an attempt to kill Aljabri in Canada, directed from Saudi Arabia. None of the scant allegations pertaining to the United States establishes the contacts between the Crown Prince, the United States, and Aljabri's legal claims."

Aljabri said Prince Mohammed sent a "hit squad" to Canada, where he lives in exile, to kill and dismember him in 2018, in the same way that journalist Jamal Khashoggi was murdered in Istanbul in October that year.

The murder sparked an international outcry and tarnished the reputation of the oil-rich kingdom and the crown prince.

Aljabri said that Prince Mohammed wants him dead because he is close to rival prince and former Saudi security chief Prince Mohammed bin Nayef, and because he has intimate information on Prince Mohammed that would sour the close relationship between Washington and Riyadh.

Aljabri alleged that the prince's personal Prince Mohammed Bin Salman Abdulaziz Foundation, was used to plan and recruit participants, dubbed the Tiger Squad, inside the United States.

But the plot was allegedly detected and disrupted by Canadian police before they could act.

In four parallel filings earlier this week, the foundation and 11 Saudis named in the lawsuit likewise sought dismissal, citing the lack of evidence and jurisdiction.

Aljabri filed the case as a claim of attempted extrajudicial killing under the Torture Victim Protection Act, and asked for unspecified personal damages for "severe emotional distress," anxiety and hypertension, and other ailments, and punitive damages as well.

But the motions for dismissal rejected that.

"Aljabri is alive and, according to the complaint itself, has never been so much as touched. By its plain terms, the TVPA does not reach an attempt at an extrajudicial killing," it said.

It also faulted Aljabri for not pursuing the case in Canada or Saudi Arabia.

The prince's filing meanwhile accused Aljabri and his family of taking part in the misappropriation and theft of $11 billion meant for counterterrorism operations when Aljabri was a senior official at the Saudi Interior Ministry in 2001-2015.

"The flaws in this complaint are so apparent and run so deep that it can only be regarded as an attempt to divert attention from plaintiff's massive theft," it said.

"Plaintiff can say whatever he wants to the newspapers. But this case does not belong in federal court."