An Israeli spyware company advised by Cherie Blair has been blacklisted by the US Government following claims that foreign administrations have used its technology to snoop on activists and dissidents.

The US Commerce Department added NSO Group, whose technology is notorious for burrowing into smartphones without users’ knowledge, to an “entity list”, saying its activities threatened national security.

Members of the entity list, which include the Chinese telecoms giant Huawei, are restricted from buying from American companies. 

Ms Blair, wife of former prime minister Tony Blair, was hired as an “external adviser” to NSO Group through her firm Omnia Strategy, amid growing controversy over its software. 

A senior judge recently found that NSO’s “Pegasus” technology was used by Sheikh Mohammed bin Rashid Al Maktoum, the ruler of Dubai, to hack the phone of his ex-wife and her lawyer, Baroness Shackleton.

Human rights groups said the company’s technology was also found on phones belonging to dozens of journalists and activists, despite NSO’s claim that it requires customers to use the technology to fight crime.

Pegasus allows hackers to eavesdrop on phone calls or access their photos and camera, and is known as one of the most sophisticated hacking tools available to governments.

NSO was added alongside another Israeli firm, Candiru. 

The Commerce Department said: “NSO Group and Candiru were added to the Entity List based on evidence that these entities developed and supplied spyware to foreign governments that used these tools to maliciously target government officials, journalists, businesspeople, activists, academics, and embassy workers. 

“These tools have also enabled foreign governments to conduct transnational repression, which is the practice of authoritarian governments targeting dissidents, journalists and activists outside of their sovereign borders to silence dissent. Such practices threaten the rules-based international order.”

It also added Russia’s Positive Technologies and Singapore’s Computer Security Initiative Consultancy to the list.

NSO Group and Omnia have been contacted for comment.