Russia was enraged by the freezing of the bank account of the Russia Today news agency in Britain.
The Russian Foreign Ministry on Monday protested that it was not informed or warned of the account's suspension, adding that the move would "hinder the activity of Russia's largest news agency" in Britain.
"No notice or warning was received by the (news) agency, its representatives have not been informed about the fate of the funds on the account," the ministry said in a statement.
"Russia has demanded that the British authorities urgently explain the situation around the closure of the RT representative office's account with Barclays in London," the ministry said.
Margarita Simonyan, editor-in-chief of Russia Today, said that the closure was illegal since the agency had not been the subject of any sanctions, although its General Director Dimitry Kiselyov had been banned from having personal accounts in British banks.
The closure of the agency's account was likely to be tied to Western sanctions against Kiselev, who is one of the people subject to financial and travel bans in the EU. These restrictions have been imposed on a number of Russian officials in connection with Moscow's alleged role in the Ukraine crisis.
"Our information is that the account was closed because of the sanctions imposed on RT General Director Dmitry Kiselyov," the ministry said.
Kiselyov was targeted by the March 21 list as a "central figure of the government propaganda supporting the deployment of Russian forces in Ukraine."
Kiselyov himself strongly criticized the British authorities' move, labeling it censorship and direct interference with the work of journalists.
"To close the account of one of the world's leading news agencies is censorship, the direct obstruction of journalists' work," Kiselyov said. "What kind of press freedom and democracy can Britain claim to have if it prevents one of the world's largest news agencies from working in the country?"
Russia's ambassador in Britain, Alexander Yakovenko, tweeted that the move is an example of using censorship against media that provide an alternative voice.
"What happened can only be regarded as an attempt at censorship, the desire to block the work of the media which are giving a platform to alternative points of view to the local official line," said the ambassador.
On Tuesday, a senior Russian lawmaker proposed blocking the bank account of the BBC in Russia as a tit-for-tat measure.