Ofcom said it had "observed a significant increase in the number of programmes on the RT service that warrant investigation" under its broadcasting code.

Separately, the parent company of Facebook, Meta, will restrict access to RT and another Russian media outlet, Sputnik, on its platforms across the European Union.

The company said it had received requests from a number of governments and the EU to take steps in relation to Russian state-controlled media on its platforms.

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The Ofcom investigations relate to 15 editions of the hourly news programme that was broadcast on 27 February between 5am and 7pm, the regulator said.

Ofcom also said it expects "full co-operation" during the inquiry into RT, previously known as Russia Today.

Its chief executive Dame Melanie Dawes said: "Given the scale and gravity of the crisis in Ukraine, audiences expect to be able to trust and rely on duly impartial broadcast news.

"When reporting on an armed conflict, we recognise it can be difficult for broadcasters to verify information and events, but it is imperative that they make every effort to do so.

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"They must also explain clearly to audiences where there is uncertainty or where events are disputed.

"Supporting a fair and free media is central to Ofcom's work. We take this responsibility - and our duty to protect audiences and uphold trust in news - extremely seriously.

"Given the serious ongoing situation in Ukraine, we will be concluding our investigations into RT as a matter of urgency."

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Prime Minister Boris Johnson criticised the Russian TV network yesterday and called for an Ofcom review.

Ofcom was also told by Culture Secretary Nadine Dorries to review the operation of RT, which she said was "demonstrably part of Russia's global disinformation campaign".