Prime Minister Justin Trudeau has linked the recent expulsion of four Russian diplomats to last year's alleged smear campaign directed against Foreign Affairs Minister Chrystia Freeland.

He offered it up as evidence of attempts to interfere with democracy in Canada, but stopped short of directly accusing the individuals who have been ordered out of the country.

Also, Trudeau carefully chose not to accuse the government of President Vladimir Putin of orchestrating the sometimes virulent social media campaign against Freeland, which played off historical material that showed her maternal Ukrainian grandfather was the chief editor of a Nazi newspaper in occupied Poland during the Second World War.

Instead, he pointed the finger at shadowy proxies.

"I think we can all remember the efforts by Russian propagandists to discredit our minister of Foreign Affairs in various ways through social media and sharing scurrilous stories about her," he said following a meeting with NATO Secretary General Jens Stoltenberg — who warned several Ottawa audiences Wednesday of the danger of Russian disinformation campaigns.

"There are multiple ways in which Russia uses cyber and social media propaganda to sway public opinion to try and push a pro-Russia narrative."

The expulsions were announced last week as part of a broader international response to the poisoning of an ex-Russian spy and his daughter in Britain with a nerve agent.

In doing so, Canada's Global Affairs department said the diplomats — three in Montreal and one in Ottawa — were really "intelligence officers or individuals who have used their diplomatic status to undermine Canada's security or interfere in our democracy."

Trudeau's comments are the first clear explanation for what was meant by the reference to Russian efforts to "interfere" in Canada's democracy. Both Treasury Board President Scott Brison and Defence Harjit Sajjan were vague last week when asked to describe the acts that led to the diplomats' expulsion.

Trudeau also said Wednesday that Canadian troops, deployed in Latvia as part of the NATO mission in the Baltic states, have a faced similar smear campaigns.

"Certainly our troops in Latvia are currently experiencing a wave of interference and propaganda by Russia," he said.

Tit-for-tat expulsions

Global Affairs confirmed the banished Russian diplomats have until the end of Thursday to leave the country.

Moscow has repeatedly denied being behind the poisoning of former Russian officer turned MI-6 spy Sergei Skripal and his daughter Yulia on March 4.

The Russian foreign ministry met the expulsion of its diplomats, in Canada and around the world, with a series of its own banishments. On Friday, it ordered four Canadian diplomats out of the country.

Wesley Wark, an University of Ottawa professor and one the country's leading experts on intelligence, said earlier that he didn't think the interference reference suggested that Canada had been subjected to the kind of meddling alleged to have taken place during the 2016 U.S. presidential election.

"It is meant to send a message to the Russians that we won't put up with influence operations, which can range from interfering with the diaspora community, to trying to develop influential political and business connections clandestinely, all the way to election meddling," he said.

Stoltenberg talked up NATO's own expulsion of Russian diplomats while addressing a University of Ottawa audience earlier today.

He said the use of a chemical weapon in the attempted assassination is just one of the actions through which Russia has worked to undermine "a rules-based international order."

Stoltenberg, a former Norwegian prime minister, struck a decidedly hawkish tone in his speech Wednesday before a group of students and dignitaries, including Canada's top military commander.

Still, Stoltenberg said no one should give up on diplomacy.

"We continue to strive for a better relationship with Russia," he said. "Russia is our neighbour. Russia is there to stay. We are not aiming at isolating Russia.

"It would be beneficial for us and them if we could improve the relationship between NATO allies and Russia.

The alliance, he said, "will continue to work for arms control, prevent a new Cold War, prevent a new arms race and continue to work for a political dialogue with Russia."

Stoltenberg didn't explain how that's possible in the current political climate.

His remarks came a day after U.S. President Donald Trump told the leaders of three Baltic states that nobody has been tougher on Moscow than he has, and that "getting along with Russia is a good thing, not a bad thing."

They also came on the same day Russia conducted missile tests in the Baltic region, forcing the partial closure of air space for a few hours.

Trump also has invited Putin to a still-to-be-arranged bilateral meeting at the White House.

When pressed in a later interview on CBC News Network's Power & Politics with Vassy Kapelos, Stoltenberg endorsed the idea of the meeting.

NATO Secretary General endorses Trump-Putin meeting 0:51

"That's for President Donald Trump to decide. I think it's the right thing that there's political dialogue, political contact between NATO leaders and Russia," Stoltenberg said, adding that in his previous tenure as prime minister of Norway, he had also met with Putin.

"Even during the Cold War, we worked with [Russia] on military issues, but that was not despite Norway's membership in NATO but it was actually because of it.

"Dialogue is not a sign of weakness. It's a sign of strength."