A senior Ukrainian envoy is warning a thaw in diplomatic relations between Canada and Russia will primarily benefit Vladimir Putin – a caution that came as relations abruptly deteriorated between Moscow and Washington on Monday over Syria and nuclear arsenals.

Vadym Prystaiko, deputy foreign minister of Ukraine, is visiting Ottawa this week to discuss the future of his country, where Russia has controlled the Crimean peninsula since 2014, and bankrolls pro-Moscow militants that have destabilized eastern Ukraine.

Mr. Prystaiko, a former Ukrainian ambassador to Canada, said Kiev is grateful for all Canadians have done for his country, but is not happy to see the Trudeau government resume co-operation with Russia over the Arctic.

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Canada and Russia are members of the Arctic Council, but the former Conservative government suspended all but low-level discussions with Moscow after the country annexed Crimea.

The Liberals announced last week that Canada and Russia will host an Arctic conference in Ottawa in November, saying shunning Moscow was an "irrationality" and illogical given that "between us we control 75 per cent of the North." Foreign Minister Stéphane Dion says Canada will continue to voice "profound disagreement" over Russia's conduct in Ukraine, noting Ottawa has increased sanctions on Moscow since the Liberals took power.

Mr. Prystaiko said engaging with Russia chips away at the international isolation that has bedevilled Mr. Putin since he took over Crimea. Russia was ejected from the Group of Eight forum of major industrialized countries and faces damaging sanctions.

"The Arctic Council is another way where [the Russian President] can break through the worldwide political blockade," the Ukraine envoy said. "The guy is going for something else than just … the fate of seals or spills of oil."

The Ukrainian official warned Canada cannot trust any of Russia's commitments at the Arctic Council.

"Any rapprochement with Russians, before they behave in a civilized way, is too premature," Mr. Prystaiko said. "Whatever the forum ... we are talking to the aggressor."

Mr. Prystaiko pointed to Mr. Putin's announcement on Monday that Moscow will suspend a treaty with Washington on cleaning up weapons-grade plutonium.

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"How can you believe in the Arctic Council or document signed with Russia if they would break any agreement?

Russia's move came just before the United States announced it was suspending one-on-one talks with Moscow toward ending the violence in Syria. Washington accused Moscow of not living up to its commitments under a ceasefire agreement.

Mr. Putin issued a decree suspending an accord concluded in 2000 that had committed the United States and Russia to shrink their nuclear arsenals and dispose of surplus plutonium originally intended for use in nuclear weapons.

The Kremlin said it was taking that action in response to unfriendly acts by Washington.

Under the Conservatives, Ottawa sent military trainers to western Ukraine to help that country's soldiers upgrade their skills for the conflict in eastern Ukraine. The deployment is slated to end in 2017, but Ukraine hopes the Liberals will extend the mission. Several years ago, Ottawa gave Ukraine $400-million in low-interest loans and has donated tonnes of non-lethal military equipment. Canada also recently concluded a free-trade agreement with Ukraine.

Pro-Russian militants retain control of a portion of eastern Ukraine where Mr. Prystaiko said Moscow posted 6,000 soldiers to lead and support the rebels. The ruble is a circulating currency in this region, he said, and Kiev charges that Russia has been stealing valuable factory equipment and metallurgical coal from the area.

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Furthermore, the conflict has blocked the most direct route for Ukraine's exports to Asia.

"Imagine the United States is [going after you] you with military force, cutting out all trade you have with the United States and then they will decide to block, for example, exports to China," Mr. Prystaiko said. "We used to send all our exports to China through the railroads over the Russian territory. Now they are blocking exports."

With a report from Reuters