Brussels, April 30 (Inditop) NATO has expelled two Russian diplomats based in Brussels in connection with a spying scandal involving an Estonian official jailed for passing top secret documents to Moscow, alliance diplomats confirmed Thursday.

One of the expelled officials is the son of Vladimir Chizhov, the Russian ambassador to the European Union (EU).

Both men were attached to Russia’s mission to NATO, which like the EU is based in Brussels. And according to a report in Thursday’s Financial Times, both had been working in the Belgian capital as undercover agents.

NATO officials would neither confirm nor deny the report to DPA.

The Russian government, meanwhile, called the move a “gross provocation” on the part of the alliance, and said it would react accordingly.

“This outrageous act contradicts in essence the NATO leadership’s declared aim of working towards normalising relations with Russia,” the foreign ministry of Russia said.

Despite the incident involving his son, Russian ambassador Chizhov would remain in Brussels, sources in Moscow said.

The expulsions come at a sensitive time for NATO-Russia relations, with the news being released just a day after ambassadors from both sides held their first face-to-face talks since last summer’s war between Russia and Georgia.

Those talks, designed to prepare a meeting of Russian and NATO foreign ministers in May, had delivered a “positive spirit of compromise”, NATO spokesman James Appathurai said Wednesday.

According to the Financial Times, the two Russian diplomats were not directly involved in the Estonian spy affair. But they were nevertheless expelled in retaliation over the Cold War-style scandal.

In February, Estonian official Herman Simm was convicted of treason and jailed for 12 years for leaking thousands of pages of secret NATO documents to Russia in a case dubbed “the biggest spy scandal in NATO history”.