U.S. President Barack Obama has chided Russia for its use of "brute force" in Ukraine and vowed that the determined alliance of the United States and Europe will prevail over time.
Obama spoke of the unity of Europe that emerged after two world wars and again the Cold War, and said the contest of ideas that led to those conflicts had emerged again.
"I come here today to insist that we must never take for granted the progress that has been won here in Europe and advanced around the world, because the contest of ideas continues for your generation and that's what's at stake in Ukraine today," Obama said.
Obama said Russia's actions in Ukraine represented a global "moment of testing."
He said the United States and Europe had no interest in controlling Ukraine, and that the United States and NATO were not seeking conflict with Russia. And Obama dismissed the idea another Cold War was starting because of Russia's actions in Crimea.
"After all, unlike the Soviet Union, Russia leads no bloc of nations, no global ideology," he added. "The United States and NATO do not seek any conflict with Russia."
Obama conceded there was no way to dislodge Russia from Crimea, but he added that so long as the United States and its allies remained united, "the Russian people will recognize that they cannot achieve security, prosperity and the status they seek."
He said it would be irresponsible to ignore what is happening in Ukraine, given Europe's history during the last 100 years. "That kind of casual indifference would ignore the lessons that were written in this continent," he explained.
Obama vowed to continue imposing sanctions on Russia if it makes further moves into Ukraine. And he repeated warnings that "if the Russian leadership stays on its current course, together we will ensure that this isolation deepens."
Earlier on March 26, during a visit to EU headquarters in Brussels, Obama said that "Russia stands alone" after Moscow's recent conduct in Ukraine's Crimean Peninsula
"Russia's actions in Ukraine are not about just one country," he said. "They are about the kind of Europe and the kind of world that we live in."
At a news briefing with EU President Herman Van Rompuy and European Commission President Jose Manuel Barroso, Obama emphasized the strong ties between the United States and Europe, saying that these are now stronger after Russia's actions in the Crimea.
"The United States and Europe are staying united on this issue," he said. "We are united in our support for Ukraine and for the need to provide economic assistance to help stabilize its economy. We are united in our commitment to Europe's security, we are united in our determination to isolate Russia and impose costs for Russia's actions."
WATCH: U.S. , EU Presidents Barack Obama and Herman Van Rompuy speak in Brussels.
Obama said Russia's leadership appeared to have underestimated the strength of the bonds between the United States and its allies in Europe.
"If anyone in the Russian leadership thought that the world wouldn't care about their actions in Ukraine, or that they could drive a wedge between the European Union and the United States, they clearly miscalculated," he said.
Barroso said the European Union and United States are coordinating their activity, not only regarding Ukraine but on other issues, to ensure a clear message is sent and understood about the price that will be paid for defying international law.
"The European Union and the United States are working together to make sure that actions that are unacceptable will bear serious consequences," he said. "And, in fact, we can say that it is in this spirit that we have not only been working on issues on Iran or the Middle East peace process, but most recently on the crisis in Ukraine."
Van Rompuy noted some positive signs from Moscow recently and encouraged more from Russia, but warned that the Kremlin could expect to face further difficulties if it does not heed the calls of the international community.
"Russia's support for an OSCE [Organization for Security and Cooperation in Europe] mission in Ukraine is a positive step," he said. "The fact that Russia's and Ukraine's foreign ministers finally met in The Hague is another sign of more openness. However, if there is further escalation, we Europeans and Americans are ready to intensify sanctions with the understanding that sanctions are a means to an end."
Van Rompuy also announced talks on new agreements with two former Soviet republics have been fast-tracked.
"We also stand by Georgia and Moldova and the European Union has brought forward to June the signing of the association agreements with them," he said.
However, all three presidents noted imposing sanctions on Russia will present economic challenges to the people of Europe and the United States, particularly as concerns energy supplies.
Obama said the United States would do what it could to help its allies in Europe to meet their energy needs but he added Europe needs to look at its own energy assets, "not just at us," as the continent seeks ways to diversify its energy supplies.