President Barack Obama is condemning a referendum for Ukraine's Crimea to become part of Russia. The vote is expected to take place March 16.
"This is our response to the disorder and lawlessness in Kiev," Sergei Shuvainikov, a member of the local Crimean legislature, said. "We will decide our future ourselves."
But the president said the move would "violate the constitution and violate international law."
"Any discussion about the future of Ukraine must include the legitimate government of Ukraine," he said. "In 2014, we are well beyond the days when borders can be redrawn over the heads of democratic leaders."
Watch President Obama's full statement on Ukraine.
Some Crimean residents also took a dim view of the upcoming referendum.
"I think that we have to stay with Ukraine, not separating, not go to Russia," Crimean student Ksenya Roshyna said.
"This is crazy. Crimea has become Putin's puppet," resident Viktor Gordiyenko, 46, said. "A referendum at gunpoint of Russia weapons is just a decoration for Putin's show. A decision on occupation has already been made."
Meanwhile, Washington is rushing to impose stiff sanctions on Russia, whose troops have seized control of Ukraine's Crimean Peninsula.
The State Department announced visa bans on pro-Russia opponents of the Ukrainian government. And the Treasury Department announced financial penalties for those who undermine Ukraine's new democracy.
The U.S. is also moving to increase the scope of international observers in Ukraine.
"We find the fact that the monitors have had extreme difficulty getting into Crimea, in performing their activities in Crimea, is very worrying. It's something that we consider unacceptable," Deputy Assistant Secretary of State Eric Rubin said.
The Pentagon is now sending six extra fighter jets to the region to monitor any Russian air space violation.
In addition, NATO is suspending plans for a joint mission with Russia.
"We have put the entire range of NATO-Russia cooperation under review," NATO Secretary-General Anders Fogh Rasmussen said.
Despite the mounting pressure, however, there's no indication that diplomatic talks with Russia are progressing.
There's also growing concern that Moscow will press forward into areas of eastern Ukraine as part of a grand plan to create a Eurasian union.
Ukraine, with its 46 million people, could help make that happen and also help Moscow pull more former soviet satellite states back into its orbit.