UK media regulator Ofcom has launched 15 investigations into Russian state-backed news channel RT's coverage of the conflict in Ukraine.
The watchdog will examine whether the channel, formerly known as Russia Today, has broken impartiality rules.
Last week, the government asked Ofcom to review RT's UK broadcasts, saying it "is demonstrably part of Russia's global disinformation campaign".
Ofcom has the power to revoke broadcast licences.
At the weekend, the European Union announced it would ban the channel.
Ofcom said it had noticed a "significant increase" in the number of programmes warranting investigation under its broadcasting code.
The 15 investigations relate to every hourly edition of the channel's News programme broadcast between 05:00 and 19:00 GMT on Sunday.
They would be conducted swiftly "given the severity and urgency of the current crisis", a statement said.
Ofcom 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."
She said freedom of expression was "a cornerstone of our approach", adding: "Given the serious ongoing situation in Ukraine, we will be concluding our investigations into RT as a matter of urgency."
A ban on RT would be likely to bring retaliatory action against British broadcasters in Russia, Foreign Secretary Liz Truss told the House of Commons on Monday.
"We are looking at what can be done on RT but the reality is that if we ban RT in the United Kingdom, that is likely to lead to channels like the BBC being banned in Russia," she said.
"What we want is the Russian population to hear the truth about what Vladimir Putin is doing, so there's a very careful judgement to be made, and that is something the culture secretary is looking at."
Last week, RT said the UK government was interfering in institutions like Ofcom that were supposedly free from political pressure.
In 2019, Ofcom fined RT £200,000 for "a serious breach" of impartiality rules in its reporting of the Salisbury poisonings and the conflict in Syria.
RT says it is an "autonomous" operation financed by the Russian Federation.
It is available in the UK via Freeview and subscription services, and broadcasts in many other countries around the world.