Ukrainian presidential adviser Mykhailo Podolyak said on Friday that Kyiv had nothing to do with Friday's attack by gunmen at a Moscow concert hall.

"Let's be straight about this: Ukraine had absolutely nothing to do with these events," Podolyak said in a video message posted on Telegram.

"We have a full-scale, all-out war with the Russian regular army and with the Russian Federation as a country. And regardless of everything, everything will be decided on the battlefield," Podolyak said.