Bank accounts belonging to Russia's state broadcaster Russia Today have been frozen in the UK.
The network's editor-in-chief, Margarita Simonyan, tweeted the news: "Our accounts in the UK have been closed. All accounts. 'The decision is not subject to revision'.
She added: "Long live freedom of speech!"
A statement on the broadcaster's website said NatWest informed RT UK "it will no longer have the broadcaster among its clients".
In a letter to RT's London Office, NatWest said: “We have recently undertaken a review of your banking arrangements with us and reached the conclusion that we will no longer provide these facilities."
The bank also said the Royal Bank of Scotland Group, which NatWest is a part of, would refuse to serve Russia Today.
Later on Monday, the bank said in a statement that such decisions "are not taken lightly". It added: "We are reviewing the situation and are contacting the customer to discuss this further. The bank accounts remain open and are still operative.”
“We have no idea why it happened, because neither yesterday nor the day before yesterday, nor a month ago, nothing special happened to us, nobody threatened us in any way," Ms Simonyan told the RBK business news website.
"Hypothetically, this may have something to do with new British and American sanctions against Russia, which may be announced soon. It may not. Our legal department is dealing with the issue now."
However, it appears that Natwest made the decision independently, with the Government not having placed any new sanctions on Russia that must be followed by UK banks since 2015.
In a post on Facebook, Russian Foreign Ministry spokeswoman Maria Zakharova said: “Britain on its way out of the EU abandoned all its commitments to protect the freedom of speech.”
She gave no information on why the accounts have been frozen.
A spokeswoman for Russia Today said: "RT has received a letter from Natwest, part of the Royal Bank of Scotland Group, which has a significant shareholding by the UK Government, informing it that its UK banking facilities with the bank will be withdrawn without explanation or redress.
"This decision is incomprehensible, and without warning.
"It is, however, not at odds with the countless measures that have been undertaken in the UK and Europe over the last few years to ostracize, shout down, or downright impede the work of RT."
She added: "RT UK will continue its operations uninterrupted."
RT, originally known as Russia Today, is a television network and news website funded by the Russian government.
It was previously sanctioned by Ofcom for biased or misleading reports on the conflicts in Ukraine and Syria.
Earlier this year the network was accused of censoring footage of Russian jets in Syria to cover up the use of incendiary bombs.
The clip was later reinstated, with RT saying it had been removed over concerns for a pilot.
The site recently accused the Daily Star and the Daily Mail of manufacturing a panic about World War Three.
"An unconfirmed report in a regional news site appears to be enough for British tabloids to remind readers how ‘Big Bad Vlad’ secretly wants to nuke them," the broadcaster said.
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