The United States considers Ukraine a sovereign state that has the right to conduct independent policies, Philip J. Crowley, Assistant Secretary of the Bureau of Public Affairs of the U.S. Department of State, has said, commenting on a letter by Russian President Dmitry Medvedev to his Ukrainian counterpart Viktor Yuschenko.

"Well, first of all, on the subject of Ukraine - it is a sovereign country. It has the right to pursue its interests in any way that it chooses. I think [U.S.] Vice President [Joe] Biden made that clear during his recent visit to Ukraine," he said.

"It is important for Ukraine and Russia to have a constructive relationship. I'm not sure that these comments are necessarily in that vein. But going forward, Ukraine has a right to make its own choices, and we feel that it has a right to join NATO if it chooses."

"And, obviously, we support that right," Crowley added.