Both Canada and NATO have protested against the expulsions, announced by Russia's Foreign Ministry on Wednesday in retaliation against a similar step by the Western military alliance last week.
"The usual practice is for diplomats stripped of their accreditation to be given time to leave the country," the source told RIA Novosti. The period is "usually it is about a week, to give the diplomat time to prepare for departure."
The diplomats have had their accreditation terminated, but are not barred from the country.
"It is not a declaration of the diplomats as persona non grata, it is merely a cancelling of their accreditation, used in diplomatic relations as a means of expressing discontent," he said.
Russia's Foreign Ministry earlier said that decision was "a response to an unfriendly act on the part of NATO in relation to staff at the Russian mission to NATO."
NATO called Russia's decision "very unfortunate and counterproductive", while Canadian Foreign Minister Lawrence Cannon called it "strange" considering NATO's recent steps to re-engage Russia.
Last week, NATO cancelled the accreditation of two Russian representatives at the alliance's Brussels headquarters, in connection with a spying scandal in Estonia.
In late February, a former head of security at the Estonian Defense Ministry was jailed for selling secret NATO documents to Russia. Investigators said Herman Simm passed nearly 3,000 documents to Russian intelligence.
Relations between Russia and NATO, which were broken off after last August's war between Russia and Georgia, have been further strained by NATO-led military exercises which began on Wednesday in Georgia.
Russia has warned that the Cooperative Longbow/Cooperative Lancer 2009 command-and-staff exercise could encourage President Mikheil Saakashvili's regime to carry out new acts of aggression.
