Obama's remarks to the press came hours after he signed an executive order that authorises sanctions on individuals and entities responsible for violating the sovereignty and territorial integrity of Ukraine or for stealing the assets of the Ukrainian people.
"The State Department has also put in place restrictions on the travel of certain individuals and officials. These decisions continue our efforts to impose a cost on Russia and those responsible for the situation in Crimea. And they also give us the flexibility to adjust our response going forward based on Russia's actions," Obama said.
The President said: "The proposed referendum on the future of Crimea would violate the Ukrainian constitution and violate international law. Any discussion about the future of Ukraine must include the legitimate government of Ukraine. In 2014, we are well beyond the days when borders can be redrawn over the heads of democratic leaders.
Let international monitors into all of Ukraine, including Crimea, to ensure the rights of all Ukrainians are being respected, including ethnic Russians; begin consultations between the government of Russia and Ukraine, with the participation of the international community, he added.
"Russia would maintain its basing rights in Crimea, provided that it abides by its agreements and respects Ukraine's sovereignty and territorial integrity. The world should support the people of Ukraine as they move to elections in May," Obama said.
"Meanwhile, we've taken steps to reaffirm our commitment to the security and democracy of our allies in Eastern Europe, and to support the people of Ukraine," he said.
The President said: "Today, the world can see that the United States is united with our allies and partners in upholding international law and pursuing a just outcome that advances global security and the future that the Ukrainian people deserve. That's what we're going to continue to do in the days to come until we have seen a resolution to this crisis.
