Russia on Tuesday accused Britain of seeking a political confrontation but stopped short of an immediate tit-for-tat expulsion of diplomats over the Litvinenko murder.
Keeping Britain guessing, the Russian deputy foreign minister, Alexander Grushko, said Britain's sanctions were "being used to politicise the Litvinenko affair". However, he warned the expulsions would "hamper anti-terror co-operation" with Britain.
Russia's move followed Britain's expulsion of four Russians after Moscow refused to extradite the prime suspect in the polonium-210 poisoning of the former Russian spy Alexander Litvinenko.
A Russian embassy source told the Russian news agency Interfax that British authorities had given the diplomats 10 days to leave the country.
He refused to name them, but said they occupied middle ranking positions.
Earlier the Russian resources minister, Yuri Trutnev, signalled Moscow's intention to shelter Russia's economic ties to Britain from the diplomatic storm.
“We will continue working as usual and don't see any reason to review our approach to foreign investments on the back of recent events,” Russian news agencies quoted the minister as saying.
This afternoon's statement came after the foreign secretary, David Miliband, yesterday set out the four expulsions as a demonstration of the “seriousness” with which Britain viewed Moscow's refusal to extradite Andrei Lugovoi, a former KGB agent, to stand trial for Mr Litvinenko's murder.
Mr Miliband told the Commons the response was "proportional and it is clear at whom it is aimed". The four Russian diplomats are officers with one of the successor organisations to the KGB, a signal that Britain suspects Russian intelligence agencies had a hand in the murder.
In Moscow, Russia's pro-Kremlin press laid the blame for the crisis on London "and the hypocritical" government of Gordon Brown.
On its front page the newspaper Isvestiya said Britain had "declared war on Russia" next to an unflattering photo of an open-mouthed Mr Brown attempting an overambitious smash with a tennis racket.
"The language of ultimatums, threats and demarches will hardly help British authorities in their dialogue with Russia," the paper said.
It added: "The actions of Gordon Brown and his newly formed cabinet are nothing but a policy of double standards."
In an interview with the paper Mr Lugovoi - the man sought for extradition by the UK - dismissed claims that he poisoned Alexander Litvinenko at London's Millennium hotel on November 1. Over the weekend waiter Norberto Andrade told the Sunday Telegraph that Mr Lugovoi had slipped radioactive polonium into Litvinenko's tea "turning the teapot yellow and gooey".

But Mr Lugovoi told Isvestiya: "It's laughable. [Mr Andrade's] claims are either a lie or stupidity. We did not look conspicuous and left after about 15 minutes. No matter how experienced the waiter might have been, it's strange that he should remember us for so long."

Most ordinary Russians seemed unmoved by the crisis.

"This isn't a big crisis, it's a medium-sized one," Natasha Trusova, a 35-year-old newspaper courier, told the Guardian. "Generally Russians think that the UK is a peaceful country, while the US is an aggressive one."

Others expressed sympathy with the Kremlin's hard-line stance.

"All intelligence services go round killing traitors. It's natural," Andrei Sakharov, 31, a project manager, said.