OTTAWA -- Russia is using a post-Cold War agreement to conduct an aerial surveillance mission over Canadian military facilities this week, even as relations between the two countries remain frosty.

The five-day mission started Tuesday and involves an unarmed Russian aircraft flying to different parts of the country to take photos of Canadian Forces bases and other military installations.

It is being conducted under the terms of the Treaty on Open Skies, which Canada, Russia and 32 other countries signed in 1992 to encourage trust and openness about each country's military capabilities and activities.

National Defence spokesman Patricia Brunelle said in an email that the Canadian military will escort the Russians across the country to ensure they don't stray beyond what is allowed in the treaty.

Canadian personnel will be aboard the plane during actual observation flights to, in part, "monitor imaging equipment, ensure adherence to the agreed flight route and profile, and provide oversight, guidance and assistance."

National Defence would not say exactly which bases or installations the Russians would be flying over for security reasons, referring questions to the Russian Embassy in Ottawa.

The embassy did not immediately return requests for comment.

Such flights aren't uncommon, with Canada having conducted its own monitoring mission over Russia this past November.

But this mission comes at a time when relations between Moscow and the West, including Canada, have reached what U.S. Secretary of State Rex Tillerson recently called "a low point."

Prime Minister Justin Trudeau called out the Kremlin earlier this month for supporting the Syrian government, which has been blamed for a chemical attack that killed more than 80 people on April 7.

More than 450 Canadian troops are also preparing to head to Latvia in the next few weeks, where they will lead a NATO force intended to check Russian aggression in eastern Europe.

And Foreign Affairs Minister Chrystia Freeland remains on a list of individuals banned from visiting Russia, after Canada slapped the country with sanctions for annexing Crimea in 2014.

Brunelle said signatories are legally obligated to allow surveillance flights under the terms of the treaty, meaning the Russians don't have to ask permission to undertake such a mission.

"The treaty is designed to enhance mutual understanding and confidence by providing all participants with the legal mechanism and technical means of acquiring, through direct observation, information about military forces and activities of concern to them," Brunelle said.

"This is done as part of the confidence and security-building measures that are designed as a mechanism to reduce hostilities and tensions between nations."

A number of agreements between Russia and the U.S. have been broken in recent months or are in danger of being broken, including a ban on cruise missiles in Europe and one treaty on nuclear disarmament.

"So the fact that we are still buying into these overflights is a good thing," said Steve Saideman, a political scientist at Carleton University`s Norman Paterson School of International Affairs.

"And given our relations with the Russians today, we should be trying to support all the opportunities you can to address the lack of confidence and trust between the two sides."