Russia's missile strikes on central and western Ukraine show Moscow is "desperate", an advisor to Ukrainian president Volodymyr Zelenskyy has told Euronews.
At least 19 people were killed and 105 wounded in Monday's attacks, which saw missiles hit Kyiv and other key cities in Ukraine.
Missile strikes continued in central and western Ukraine on Tuesday.
Russia's president, Vladimir Putin, commenting on Monday's missile strikes, said they were a retaliation for the blast on a key bridge linking Russia with Crimea, territory it annexed from Ukraine in 2014.
"We can certainly tell that this is retaliation, it's revenge for the Ukrainian successes that we've had, both on the frontlines and also in terms of what happened to the bridge in Crimea," said Alexander Rodnyansky, advisor to Ukraine's president.
"Now, remember, there is no direct proof, no consequential [nor] direct evidence that it was actually Ukraine that blew up the bridge. So that tells you a lot about what might be going on within Russia. You know, it remains to be seen.
"But ultimately, yes. I mean, the Russian leadership is desperate. They don't know what to do next. They're trying to escalate as far as they can in order to freeze the frontline because they can see that they're losing ground day by day."
Watch the full interview with Rodnyansky in the video, above.