Russia ordered the removal of the first secretary at the Canadian embassy in retaliation for the expulsion of a Russian military attache from Ottawa earlier this month, said a Canadian government source, not authorized to speak on the record.
The Harper government also called in the Russian ambassador for a diplomatic dressing-down last week as pro-Russian gunmen seized government buildings in several eastern Ukrainian cities following Russia's annexation of the Crimean Peninsula last month.
Canada has imposed economic and political sanctions against Russia.
Ambassador Georgiy Mamedov fired back on Tuesday, telling an audience at the Empire Club in Toronto that Canada had started a "sanctions war" against Russia that would have limited effect.
Mamedov said Crimea has always belonged to Russia and said Russians faced discrimination in Ukraine.
Mamedov was heckled by an audience member who shouted "not true," while another held up a sign that read, "Lies." The envoy pleaded with the hecklers to let him have his say.
As he began a week-long tour of eastern Europe in the Czech Republic on Tuesday, Foreign Affairs Minister John Baird reiterated the Harper's government's condemnation of Russia.
"We will stand with you in the face of aggression," Baird said after meeting his Czech counterpart in Prague.
Prime Minister Stephen Harper sent Baird to several eastern European countries to stress Canada's support, after calling Russia's actions in Ukraine a threat to world peace. Harper said the pro-Russian groups in eastern Ukraine were "Russian provocateurs sent by the Putin regime.''
Baird will also visit Slovakia, Poland, Latvia and Estonia.
Meanwhile, Harper spoke by telephone Tuesday with Prime Minister Iurie Leanca of Moldova.
The two discussed the situation in Ukraine and Eastern Europe. They both condemned Russia's actions in Ukraine and Harper reaffirmed the importance of Moldova maintaining its sovereignty within internationally recognized borders.
Last week, Canada announced the contribution of six CF-18 fighter-bombers to a NATO air-policing mission to be based in Poland.
"We will be making other announcements of specific projects in the coming days," Baird said Tuesday.
Canada and Poland are to announce a joint assistance package for Ukraine when Baird arrives in Poland on Thursday.
Marcin Bosacki, the Polish ambassador to Canada, recently told The Canadian Press that the assistance would include measures to strengthen Ukraine's democratic institutions.
Hundreds of U.S. army troops are arriving in Poland for a series of military exercises that will span four eastern European countries in show of force. The military manoeuvres will also be conducted in Estonia, Latvia and Lithuania.
As well, five NATO mine-hunting ships sailed from the German port of Kiel on Tuesday bound for the Baltic Sea, as part of the alliance's efforts to strengthen its presence in eastern Europe amid mounting worries over Russian intentions.
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