Vladimir Putin will "look seriously" at consolidating Russia's position in eastern Ukraine if the opportunity presents itself, former Secretary of State Hillary Clinton said on Wednesday.
Speaking in Florida, the potential Democratic presidential candidate said she was still in contact with some of her former government colleagues on the issue.
And she believes the United States needs to support a "unified Ukraine" with no division between the east and the west of that country.
Many are struggling to come to grips with the rapid political upheaval that has unfolded there in recent days, after months of protests and last week's bloody clashes between protesters and security forces.
There is broad divide between those who support events in Kiev, where a new government is leaning toward the West, and those who back Russia's continued influence in eastern and southern Ukraine.
Clinton said Putin is a man who "sits as the absolute authority now in Russia and it is quite reminiscent of the kind of authority exercised in the past by Russian leaders, by the czars and their successor Communist leaders."
On Ukraine, she said Putin could consider making a move.
"I believe, and this is just my opinion, if there is an opportunity for him to consolidate the position of Russia in eastern Ukraine, he will look seriously at doing that," she said.
Speaking in Washington this week, Secretary of State John Kerry said officials were "deeply engaged in trying to help this extraordinary transition that is taking place in Ukraine."