OTTAWA - Prime Minister Stephen Harper says he's "concerned" about Russia's behaviour as Ottawa calls in the country's ambassador to explain why two Canadian diplomats are being expelled from Moscow.

Russia ordered the diplomats out in retaliation for NATO's decision last week to rescind the credentials of two Russian diplomats in Brussels.

"It's true at NATO we talked of reconciliation (with Russia), but I haven't changed my view that we are concerned about Russian behaviour on a number of fronts," Harper said in Prague where he's kicking off free-trade talks with the European Union.

"I don't want to say this is the Cold War, but it's certainly not an ideal situation."

He said Canada and NATO will continue to try to "engage" Russia while also making clear its position on issues like democracy and human rights.

"When it comes to spying we will take whatever actions are necessary," he said.

"Russia has a right to retaliate but it doesn't change the fact that these diplomats were not engaged in anything illegal or unethical."

Foreign Affairs Minister Lawrence Cannon said Wednesday that he summoned Ambassador Georgiy Mamedov to explain the expulsion of Isabelle Francois, director of the NATO information office in Moscow, and her deputy, Mark Opgenorth.

"We have a very serious objection to what has occurred," Cannon said.

He, too, expressed surprise at the latest events, considering NATO's recent bid to patch up the relationship following Russia's brief war with Georgia last summer.

"I find it rather strange that this has happened considering that NATO has re-engaged with Russia.

"As you know, after the crisis in Georgia there was a break off ... in the relationship and there has been a gradual re-engagement and now we're seeing this occur."

NATO expelled two Russian diplomats from its headquarters in Brussels last week, a move Russian officials said was in retaliation for a spy case dating back to February.

Russian Foreign Minister Sergey Lavrov pulled out of a meeting with NATO scheduled for later this month to protest that move - as well as the alliance's military exercises in Georgia, which got underway Wednesday.

"This is the law of genre, and our NATO partners - those behind the expulsion - could not have expected a different reaction," Lavrov said of the Canadian diplomats.

He described the action as in keeping with "the rules of the game."

Russia is frustrated by what it sees as western meddling in its traditional sphere of influence. Moscow also opposes Georgia's efforts to join NATO.

NATO maintains the war games in Georgia are not directed at Russia.