Putin earlier said he was protecting ethnic Russians by moving troops into Crimea.
At a closed fundraising luncheon in Long Beach earlier on Tuesday,
Clinton said Putin's actions are similar to what happened in the Nazi era in Czechoslovakia and Romania.
“Now if this sounds familiar, it is what Hitler did back in the '30s,” Clinton said.
“Hitler kept saying, ‘They are not being treated right. I must go and protect my people’. And that is what has gotten everybody so nervous,” she added.
Responding to a question, Clinton said she was not making a comparison although Russia’s actions were ‘reminiscent’ of claims Germany made in the 1930s, when the Nazis said they needed to protect German minorities in Poland and elsewhere in Europe.
"The claims by President Putin and other Russians that they had to go into Crimea and maybe further into eastern Ukraine because they had to protect the Russian minorities, that is reminiscent of claims that were made back in the 1930s when Germany under the Nazis kept talking about how they had to protect German minorities in Poland and Czechoslovakia and elsewhere throughout Europe,” she said.
“I just want everybody to have a little historic perspective. I am not making a comparison, certainly. But I am recommending that we perhaps can learn from this tactic that has been used before,” she added.