Rubio, a member the Senate Foreign Relations and Intelligence committees, stopped short of asking for U.S. military intervention.
"Twenty-five years after the people in the then-captive nations of Eastern Europe changed world history, we again see Ukrainians taking to the streets to demand nothing more than the right to independently chart the future course of their nation and a better life for themselves and their children," he said.
Anti-government protesters in the Ukrainian capital of Kiev seized control of the central post office Wednesday and stood their ground against riot police on the city's main square, a day after clashes that left at least 25 people dead and raised fears of prolonged violence, the Associated Press reported.
The opposition and President Viktor Yanukovych's government are locked in a deep struggle over the identity of their nation of 46 million, which is divided in its loyalties between Russia and the West.
Rubio said the demonstrations show that Ukrainians "have made clear that they want the opportunity to be governed free of corruption and Russian pressure."
"I strongly condemn the Yanukovych government resorting to violence rather than dialogue and compromise with the opposition," he said.
"Ukraine's future lies in Europe, not Vladimir Putin's Russia. America stands with those who seek freedom even at great risk to their own security."