It came as Putin signed a treaty claiming the Black Sea region of Crimea as Russian territory, as Ukraine warned the showdown had entered a "military stage" after soldiers were killed on both sides.
The treaty signing was conducted at lightning speed in the Kremlin in a defiant expansion of Russia's post-Soviet borders that has plunged relations with the West to a new post-Cold War low.
"We've got to do a better job in supporting the government in Kiev, we've got to do a better job in getting Europe to do more for themselves when it comes to energy so they're not dependent," said Clinton, a potential 2016 Democratic US presidential candidate.
"It's an effort by Putin to rewrite the boundaries of post-World War II Europe," Clinton, also a former US first lady, told a conference organized by the Board of Trade of Metropolitan Montreal, to applause.
"I hope there's not another Cold War, obviously nobody wants to see that. Primarily, it's up to Putin."
Clinton, who narrowly lost the Democratic nomination in 2008, added: "The rationale that Putin uses (in Crimea) -- that they were ethnic Russians, Russian speakers, that they've always been part of Russia -- it could be extended not only to other parts of Ukraine but also to other parts of Estonia, Lithuania, Latvia, Transnistria.
"There are a lot of places where there are ethnic Russians and Russian speakers."
Asked whether she would run for the White House, Clinton replied: "I haven't made up my mind, besides I feel a deep sense of commitment to my country and its future. I feel an obligation to do all I can for the children of my country."