MOSCOW, Oct 19 (Reuters) - Russia has promised to retaliate against Britain after a British state-owned bank said it was withdrawing its services from Kremlin-backed Russian broadcaster RT.

RT said on Monday that NatWest, owned by Royal Bank of Scotland Group (RBS), had given notice it intended to withdraw its banking services from the channel's British arm. RT accused the bank of attacking freedom of speech.

RBS responded by saying it was reviewing the situation and would contact RT to discuss the matter, which caused a furore in Russia where the Russian Foreign Ministry said it looked like a politically-motivated move to silence an inconvenient outlet.

Maria Zakharova, the Foreign Ministry's spokeswoman, told reporters on Tuesday evening that Moscow would retaliate in kind if necessary.

"Our stance is unambiguous. We never leave friends in the lurch. Tit-for-tat retaliation is always due," the TASS news agency cited Zakharova as saying.

"Apparently, we need to reach a certain point to react and show the other side a mirror image of its own actions. To let them feel a similar situation. It works well. But this is not our choice."

She did not say which British media outlet or outlets operating in Russia might be targeted for retaliation.

Three pro-Kremlin senators in the upper house of parliament have urged authorities to hit back by closing the BBC's bank accounts in Russia, the RIA news agency reported on Monday.

(Reporting by Maria Tsvetkova; Editing by Andrew Osborn) ((; +7 495 775 1242;))