Russia's security service has accused the United States of being behind a cyberattack on thousands of Apple devices as cybersecurity firm Kaspersky Lab said it discovered spyware on iPhones used by its staff.

The FSB said on Thursday that the US National Security Agency was in "close cooperation" with Apple as thousands of devices were "infected" and that the telephone numbers of people working at Russian embassies abroad were leaked.

Separately, Kaspersky said its researchers found previously unknown malware on iOS devices and that dozens of its staff were targeted.

The antivirus software maker's founder, Eugene Kaspersky, said the devices received an "invisible iMessage" with a malicious attachment which installs spyware.

He said the spyware then "quietly" transmits private information to remote servers, including microphone recordings, photos from instant messengers, geolocation and other data.

"We're confident that Kaspersky was not the main target of this cyberattack," he said in a blog post.

The company said the oldest traces of infection date back to 2019 and that "the attack is ongoing".

US regulators designated Kaspersky a "threat to national security" in March 2022, after Moscow sent troops into neighbouring Ukraine.

Founded in 1997, Kaspersky has been accused of being close to Russian intelligence services. 

The company has 400 million customers worldwide.

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