Russia has expelled two Canadian diplomats working for Nato's Moscow office in response to an "unfriendly act" by the military alliance.
Last week Nato expelled two Russian envoys from its headquarters in Brussels, reportedly due to spying.
The diplomatic spat comes as Nato begins military exercises in Georgia, seen by Russia as a "provocation".
Last August Russian and Georgian forces clashed in a brief war over breakaway pro-Moscow Georgian territories.
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