Vladimir Putin once threatened that he could have Russian troops in six capital cities in just two days, it is claimed.
The Russian president is said to have warned former Ukrainian President Petro Poroshenko that he could have soldiers on the ground in Ukraine, Poland, Latvia, Lithuania, Estonia and Romania within 48 hours.
His forces are currently bogged down with fierce fighting after failing to secure the swift invasion of Ukraine he expected.
In his remarks, reportedly made in 2014, Putin claimed that he could have soldiers in the capitals of all six countries within two days.
German newspaper Suddeutsche Zeitung reported that the Russian president told Mr Poroshenko, who was succeeded by Volodymyr Zelensky in 2019: "If I wanted, in two days I could have Russian troops not only in Kyiv but also in Riga, Vilnius, Tallinn, Warsaw and Bucharest."
He also told Mr Poroshenko, it is claimed, "not to rely too much on the EU".
The alleged threat came after Putin reportedly said he could take the Ukrainian capital “in two weeks” as thousands of Russian troops gathered at the border.
Mr Poroshenko told the US Congress in 2014: "If they are not stopped now, they will cross European borders and spread throughout the globe."
The Kremlin later denied Putin had made the comments after they were widely reported.
Last month the Russian government falsely claimed that Russian invaders would be greeted by citizens in Ukraine, but instead have been met with strong resistance and have been unable to secure Kyiv.
It has long been feared that the Russian president plans to expand his territory into EU and NATO countries.
Earlier this month European Commission Vice President Valdis Dombrovskis warned that Putin could aim his aggression at Lithuania, Latvia and Estonia if Ukraine falls.
He said: “If we do not support Ukraine, it’s not going to stop in Ukraine.
"Clearly, Putin is now in some kind of aggressive war mood and unfortunately, it is likely that this aggression will continue in other countries."
In an interview with the Economist, current Ukrainian president Mr Zelensky said sanctions against Russia came too late, suggesting the invasion could have been prevented.
He said: “I am sure that if tougher sanctions had been levied earlier, a full-scale Russian attack would not have occurred."
Yesterday Mr Zelensky told a group of Russian independent journalists on Sunday that Kyiv was prepared to become neutral and meet Moscow on some of its demands.
It would abandon its drive to join NATO and vow not to develop nuclear weapons, on the basis that Russia would withdraw troops and give Kyiv security guarantees.
No peace deal would be possible without a ceasefire and withdrawal of troops, he said, though he ruled out trying to recapture all Russian-held territory by force, saying it "would lead to a third world war".
The aim, he said, was to reach a “compromise” over the eastern Donbas region, held by Russian-backed forces since 2014.
However, Mr Zelenskiy said Ukraine refused to discuss certain other Russian demands, such as the demilitarisation of the country.
Zelenskiy hosted a video call - which the Kremlin preemptively warned Russian media not to report - to deliver his message directly to Russian journalists on the eve of a new round of peace talks in Turkey.
The president has previously spoken in Russian in speeches aimed at a Russian audience.
The proposed meeting midway was on condition that the changes were put to a referendum and third parties promised to protect Ukraine, he said.
“Security guarantees and neutrality, the non-nuclear status of our state — we’re ready to do that.
“That’s the most important point… they started the war because of it,” Mr Zelensky said.
