The decision by U.S. President Donald Trump to fire FBI director James Comey is alarming and part of a global shift away from democratic controls over powerful people, former intelligence officer Edward Snowden said Tuesday night.

Snowden spoke via video link to three universities in Manitoba and Alberta from Russia, where he lives in exile after quitting the National Security Agency in the U.S. and revealing some of its surveillance secrets.

He said the firing is worrisome because Comey was conducting a wide-ranging probe into the Trump administration, including the possible influence of Russia in last year's U.S. election.

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"This calls into question our commitment to the rule of law," Snowden said.

"It's not to say that what the president has done is illegal, but we should not lose sight of the fact that ... the president of the United States has just fired the man in charge of a criminal investigation into the actions of his administration and his associates."

Trump's move is part of a global "creeping disrespect for the public and their rights," Snowden added. He spent part of his 40-minute speech, followed by a question-and-answer session, focusing on new surveillance laws in the United Kingdom, Russia and other countries.

Snowden mentioned the surveillance by Montreal police last year of journalist Patrick Lagace. The police force monitored Lagace's iPhone for months in order to find out who he was speaking with.

Technological advancements are outpacing the ability of democratic institutions to enact controls on surveillance and protect people's privacy, Snowden said.

He urged the audience of students, academics and others to remain vigilant and fight for greater privacy rights.

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"Privacy, when we think about these things, is the fountainhead from which all other rights derive," he said.

"For example, freedom from unreasonable search and seizure, the right to due process, to be presumed innocent until proven guilty and so on."

Snowden quit his job at the National Security Agency in 2013 and left the U.S. He revealed how the NSA conducted secret information-gathering programs and spied on the online activities of millions of people.

To some, he has become a heroic whistleblower who has exposed invasive government surveillance. To others, he is a traitor who has compromised U.S. security.

He has been charged with espionage in the U.S. and could face up to 30 years in prison if he returns there.