In an espionage tale reminiscent of a Cold War saga, two Russian diplomats have been booted out of Nato as part of an explosive spy scandal on the same day the alliance resumed formal talks with Moscow.
Russia reacted with fury to the expulsion of its envoys, one of who is reportedly the son of Moscow's ambassador to the European Union, Vladimir Chizhov, and the other a senior adviser to its Nato ambassador, Dmitry Rogozin.
They were expelled from Nato's Brussels headquarters in retaliation for a case that has been described as the biggest spy scandal in the organisation's history, officials said.
In February, an Estonian defence chief, Herman Simm, was found guilty of selling thousands of highly classified Nato documents to Russian intelligence officials for a staggering 12 years before being caught out. Mr Simm has now begun serving out a 12-year prison sentence.
The Russian duo are not thought to have any direct link to the Estonian debacle but Nato sources say the affair so badly compromised its allies' security that it required a tough response.
In a deeply embarrassing coincidence, notice of the expulsions was handed down on Wednesday night, just hours after Nato resumed ambassadorial level talks with Moscow, following an eight-month suspension triggered by Russia's five-day war with Georgia last August.
The response from Russia was furious. "A crude provocation has been made in relation to two employees of Russia's permanent mission to Nato on an absolutely trumped-up pretext without any clear explanation," its Foreign Ministry said yesterday. In Brussels, Mr Rogozin warned that the expulsions "would not go without answer" and that the response would be "harsh and decisive".
Russia has about 50 diplomats as part of its Nato mission in Brussels, which was set up in 1998 at a time when former Soviet-block states – including Estonia – began their membership applications to join the organisation. Although there have never been such public expulsions of Russian officials before, diplomats said this was not the first incident of its kind.
"People have been kicked out in the past but normally it always happens quietly and well away from public view. But in this case, someone clearly wanted to go public with it, which is why it has now grown overnight into such a big political issue," said a senior Nato official on condition of anonymity.
Daniel Korski, a security expert at the European Council on Foreign Relations, said: "We know that the Russians have increased their espionage activities massively since the end of the Cold War. The Russians cannot but react with anger. But it is unlikely that they will go any further than sabre-rattling, given that they too said they want to rebuild bridges with Washington and the West."
Barack Obama has been leading calls for a "reset" with Russia.