TV watchdog Ofcom has launched 15 investigations into the “due impartiality” of programmes on news channel RT, it has announced.

The UK regulator said it had “observed a significant increase in the number of programmes on the RT service that warrant investigation” under its Broadcasting Code.

The investigations relate to 15 editions of the hourly news programme broadcast on February 27 between 5am and 7pm, they confirmed.

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

In a statement, 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.

“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.”

On Sunday, Boris Johnson criticised the Russian television network and called for an Ofcom review.

Similarly, Ofcom had been told by Culture Secretary Nadine Dorries to review the operation of RT, which she said was “demonstrably part of Russia’s global disinformation campaign”.