Speaking in Montreal on Tuesday, Clinton said Canada and the U.S. should work together to find a smart way to prevent more conflicts or a situation that gets out of control.
"I think Canada and the United States can inject some real thoughtful analysis as to how we can deter further aggression against free people," Clinton said during a question-and-answer period that followed her speech to the Board of Trade of Metropolitan Montreal.
"A lot of your military leaders have played significant roles and I think we have to remain closely unified in trying to think of what happens next. How will we deal with what I'm afraid we're in for, which is a lot of probing and testing."
Instead of "rattling sabres," she suggested NATO proceed with its sanctions and provide timely financial and technical support to the government in Kyiv. She said the allies must also make it clear to Ukraine that it have an inclusive government.
Clinton also said steps must be taken to help European countries become less reliant on Russian energy sources.
"The Russians can only intimidate you if you are dependent on them," said the potential 2016 U.S. presidential contender.
Putin has called Sunday's referendum on Crimea, which overwhelmingly supported annexation, legal and signed a treaty Tuesday for the strategic region to become part of Russia.
Foreign Affairs Minister John Baird announced new sanctions Tuesday against Russia as he slammed Russian President Vladimir Putin over what he called the "illegal annexation" of Crimea.
Baird, who later attended Clinton's speech, said 17 Ukrainian and Russian officials were added to a list of those who had their assets frozen. He said they will also face travel restrictions.
Prime Minister Stephen Harper has called the result of the so-called referendum illegitimate, saying the vote was held under an illegal Russian military occupation. On Friday, Harper is scheduled to travel to Kyiv to show his support for the temporary government.
Clinton said Putin's actions broke international law.
She warned that Putin's rationale for annexing the Crimean Peninsula because it's home to ethnic Russians and Russian speakers could be extended not only to other parts of Ukraine, but to other countries like Estonia, Lithuania and Latvia.
"This is a clash of values and it's an effort by Putin to re-write the boundaries of post-World War Two Europe," Clinton said to nearly 4,300 people who paid between $50 and $300 to attend her event.
"I hope there's not another Cold War. Obviously, nobody wants to see that. I think that's primarily up to Putin."
Clinton's 30-minute speech focused on the importance of ensuring more women participate in the global workforce and in politics.
The former first lady, who later served as secretary of state from 2009 until 2013, was joined at the table of honour by more than two dozen guests, including the leaders of Quebec's three major political parties.
Parti Quebecois Leader Pauline Marois, Liberal Leader Philippe Couillard and Coalition leader Francois Legault took breaks from the campaign trail to attend the event. The province will head to the polls April 7.
The crowd, largely comprising business people, cheered a waving Couillard as he walked into the room before Clinton's address. Marois received a mix of cheers and boos from attendees as she entered a few moments later.
- with files from Associated Press
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