The editor-in-chief of RT, the international television network funded by the Russian government and formerly known as Russia Today, has said its UK bank accounts have been frozen amid high tensions between the two countries.
Margarita Simonyan, who runs the news channel, tweeted: "Our accounts in the UK have been closed. The decision can not be reversed. Long live freedom of speech!"
RT, which has repeatedly been criticised for alleged pro-Russia bias on its reporting of stories such as the crash of Malaysia Airlines Flight MH17, said it had been informed by NatWest that the bank had "undertaken a review of [RT's] banking arrangements" and decided to close its accounts.
According to the channel, RT had banked with NatWest for a decade and has been told its accounts will close in November and December.
"We are looking into whether this will affect the further functioning of RT in the country," said the channel's Anastasia Churkina.
In a statement the Russian Embassy in London strongly attacked the bank's decision and suggested the UK government was involved: "We are concerned over the said decision and the pressure exercised against Russian news outlets in UK (Rossiya Segodnya, Sputnik, VGTRK also had their accounts frozen or closed). That is an outrage. It makes it abundantly clear that this ham-fistedness is all HM Government can say in support of its position on the international issues where we differ.
"The Russian side will request explanations, including as regards UK's compliance with OSCE and other norms guaranteeing freedom of speech."
RBS, which owns Natwest, issued a statement late on Monday in which it appeared to suggest it was reconsidering the decision to close the accounts: "These decisions are not taken lightly. We are reviewing the situation and are contacting the customer to discuss this further. The bank accounts remain open and are still operative."
It is not clear whether the UK government was involved in the decision. The Foreign Office referred all questions to the Treasury, which has yet to respond.
Relations between the UK and Russia are currently extremely poor – foreign secretary Boris Johnson recently urged protesters to march on the Russian embassy over the country's involvement in the war in Syria.
Russian foreign ministry spokesperson Maria Zakharova said the decision showed the UK had abandoned its commitment to freedom of speech following the decision to leave the EU.