Kyiv warned that Russia may have access to personal data and messages on the app, which serves as one of the main modes of communication in both Ukraine and Russia.

"The National Security and Defence Council decided to restrict the use of Telegram in government agencies, military formations and critical infrastructure facilities," the council said in a statement on Facebook, saying it was a "matter of national security."

It added that employees who use Telegram as part of their duties will not be affected by this rule, as the app remains a major communications channel for the army and public authorities.

Intelligence chief Kyrylo Budanov said Moscow could have access to messages on Telegram, including "deleted messages as well as their (users') personal data."

He said it was "not a matter of freedom of speech, it is a matter of national security."

Security officials also said Telegram is used by Moscow for "counterattacks, spreading phishing and malware, establishing user geolocation, adjusting missile strikes etc."

A high-ranking security official told AFP that "this only applies to official communications".

"It is a big source of information leaks as Telegram is very easily hacked" by the Russian side, the source said.

The source added that "citizens can continue to use it."

Telegram's founder and boss Durov was arrested in France last month and charged with publishing illegal content on the application.

Durov is currently banned from leaving France.