The United States says it is not seeking "confrontation with Russia."
But U.S. State Department spokeswoman Jen Psaki said Washington "cannot and will not compromise on the principles on which security in Europe and North America rest."
Psaki said there may be disagreements, "but we remain committed to upholding Ukraine's sovereignty and territorial integrity."
Psaki's comments come hours after Russian President Vladimir Putin said the world is becoming an increasingly dangerous place because of what he said were U.S. attempts to enforce its will on other countries.
Putin said the United States has been "fighting against the results of its own policy" in Iraq, Libya and Syria.
Speaking at an international forum in Sochi, Putin said the West has ignored Russia's legitimate interests in Ukraine and supported the ouster of Viktor Yanukovych, the former Ukrainian leader friendly to Moscow.
The United States and European Union imposed sanctions on Russia after it annexed the Black Sea peninsula of Crimea, and allegedly armed rebels fighting for independence in eastern Ukraine.
Putin dismissed those measures as a "mistake," saying they aimed at pushing Russia into isolation and would end up "hurting everyone."
Putin accused the West of breaking promises, pointing to a February phone conversation with President Barack Obama just hours before protesters in Kyiv drove Yanukovych out of office.
Putin warned that his nation will firmly stand its ground to defend its vital interests.
"The bear is the master of the taiga (a subarctic forest). It's not going to move to other climate zones," he said. "But it's not going to give up its taiga to anyone."
"Russia is not demanding some special, exclusive place in the world," he said. "While respecting interests of others, we simply want our interests to be taken into account, too, and our position to be respected."
