Israel's justice minister on Wednesday pledged a full investigation into allegations that the controversial Pegasus spyware was used on Israeli citizens, including people who led protests against former premier Benjamin Netanyahu.

Pegasus, a surveillance product made by the Israeli firm NSO that can turn a mobile phone into a pocket spying device, has remained a source of global controversy following revelations last year it was used to spy on journalists and dissidents worldwide.

According to the business daily Calcalist, Pegasus was also used by police on citizens at the forefront of protests against Netanyahu last year, when he was still prime minister, as well as other Israelis.

Israeli police have firmly denied the report.

Public Security Minister Omar Barlev, a Netanyahu critic who took office as part of a new government that ousted him in June, offered a more nuanced defence.

There was "no practice of wire-tapping or hacking devices by police without a judge's approval", he said.

Israeli security forces have wide leeway to conduct surveillance within Israel with judicial approval.

But Tehilla Shwartz Altshuler, an expert at the Israel Democracy Institute think-tank, told AFP "you can't really ask for a court order authorising Pegasus" because Israeli law does not currently permit such invasive surveillance of its citizens.

"It is now clear that the current Protection of Privacy Law is not equipped to cope with today's reality," she said.

Smartphone shows the website of Israel's NSO Group which features 'Pegasus' spyware Smartphone shows the website of Israel's NSO Group which features 'Pegasus' spyware Photo: AFP / JOEL SAGET

The justice ministry and State Comptroller's office both said they were looking into the Calcalist reports.

The Privacy Protection Authority, a division of the ministry, said use of Pegasus to monitor Israeli citizens" would constitute a "serious violation of privacy", announcing its investigation.

State Comptroller Matanyahu Englman said Tuesday he would expand his ongoing investigation into law enforcement's use of surveillance technology to include the latest Pegasus allegations.

He would in particular probe "the balance" between the "usefulness" of surveillance tools in investigations and "violations of the right to privacy".

Justice Minister Gideon Saar, another Netanyahu rival, told parliament Wednesday that he fully backed the probes.

"There is a huge difference between the claims in the Calcalist article and the police statements," Saar told the law committee in the Knesset, Israel's parliament.

"It's good that the state comptroller, who is an independent body, took upon himself to examine the issue," Saar said.

"In the (justice) ministry we were not aware of any activity without a court order. It is good that these things will be examined, and the public will receive the conclusions."

NSO would neither confirm nor deny it sold technologies to Israeli police, stressing that it does "not operate the system once sold to its governmental customers and it is not involved in any way in the system's operation".

"NSO sells its products under license and regulation to intelligence and law enforcement agencies to prevent terror and crime under court orders and the local laws of their countries," it said in a statement sent to AFP on Wednesday.

Israel's defence ministry, which must approve all exports of Israeli-made defence industry products, has also opened an investigation into sales of Pegasus overseas.