The introduction of the new sanctions against Russia by the U.S. in relation to the case of Ukrainian pilot Nadia Savchenko would be a justified step, a leading expert of Brookings Institute in Washington, former U.S. Ambassador to Ukraine Steven Pifer has said.

He said he would support this measure if it was clearly differentiated from those which had been already introduced, namely sanctions related to the Russian aggression in Ukraine's east and the Crimean annexation, Pifer told Interfax on Thursday.

At the same time, he suggested waiting for the Russian court ruling in Savchenko's case and see what happens afterwards. Pifer said he had no doubts she would be found guilty.

He also stressed that the Russian leadership had to have a clear understanding of conditions for the sanctions to be lifted, noting that unless there were a clear distinction between various kinds of sanctions, they were unlikely to achieve a desired result.

There should be no confusion as to the steps Russia had to take to lift the sanctions, Pifer added.