One of Russian President Vladimir Putin's closest ex-advisers has claimed that the ex-KGB agent ultimately wants to reclaim Finland for Russia.

Andrej Illiaronov, Putin's economic adviser between 2000 and 2005 and now senior member of the Cato Institute think tank, said that "parts of Georgia, Ukraine, Belarus, the Baltic States and Finland are states where Putin claims to have ownership."

"Putin's view is that he protects what belongs to him and his predecessors," he said.

When asked if Putin wishes to return to the Russia of the last tsar, Nicholas II, Illiaronov said: "Yes, if it becomes possible."

Illiaronov admits that Finland is not Putin's primary concern at present but, if not stopped in other areas of Eastern Europe, the issue will one day arise. Russian troops are currently massing on the eastern border of Ukraine, following Russia's recent annexation of Crimea.

"Putin said several times that the Bolsheviks and Communists made big mistakes. He could well say that the Bolsheviks in 1917 committed treason against Russian national interests by providing Finland's independence," Illiaronov told a Swedish news website.

He believes that Putin is not planning to invade Ukraine for territorial gain but rather "the goal is a pro-Russian puppet government in Kiev."

"Six years ago Putin conquered Abkhazia and South Ossetia from Georgia. The west let him do it with impunity, and now he has got Crimea," he continued.

"Now, eastern and southern Ukraine is destablised so that the self-defence forces can take power there. If the situation allows, it may be a military invasion."

Finland was a part of the Russian Empire for 108 years but broke away in 1917 at the end of the First World War.

The Scandinavian nation was attacked at the beginning of the second world war by the Soviet Union, with Finland fighting the winter war and the continuation war in resistance and losing 10% of its pre-war territory.

Finland is not a member of Nato, so any invasion of its land would not constitute an attack against all members under Article 5 of Nato's founding Washington Treaty.