Russia is acting like a "terrorist" in Ukraine and in its intimidation of other neighbours, Lithuania's President Dalia Grybauskaite said in an interview released Thursday.

"I think that Russia is terrorising its neighbours and using terrorist methods," she told the Washington Post newspaper, replying "Yes" when asked whether she thought both Russia and the Islamic State (IS) group, which is sweeping across Syria and Iraq, were terrorists.

"The danger of Russia's behaviour today is not smaller than what we have with ISIS in Iraq and Syria," she added.

Grybauskaite, an outspoken former EU budget chief, also slammed the West for a lack of leadership in standing up both to the IS in the Middle East and Russia in Ukraine.

"Lack of leadership has allowed terrorist groups such as ISIS (Islamic State group) to grow, and on the question of Ukraine, it has allowed Russia to become a state with terrorist elements," she said.

The 58-year-old karate black-belt dubbed Lithuania's Iron Lady for her hardline on Russia also warned that if its President Vladimir Putin "will not be stopped in Ukraine, he will go further", possibly attacking formerly Soviet-ruled Baltic states now members of the EU and NATO.

Nor does she believe Putin would be deterred by NATO's Article 5 "one for all and all for one" mutual defence guarantee.

"Everybody declares that NATO's Article 5 will take place. But it will not stop Putin from his plans if he does not see real actions from the European and world leaders. They are only talking.

"We need to stop him in Ukraine. And until now, that is not understood. That is why I am saying that in Europe today, leadership is taken by Putin, not by the West," she told the Washington Post.

Grybauskaite decried the West for being "so busy not to offend Putin who is today sending his troops to kill and occupy Ukrainian territory.

"Sooner or later we will call him a terrorist and a criminal," said told the Washington Post.

Russia's annexation of Ukraine's Crimean peninsula in March rattled nerves in Lithuania and fellow Baltic states Latvia and Estonia, which were ruled by the Soviet Union throughout the Cold War.

They won independence in 1991 and joined NATO and the European Union in 2004 in a bid to secure their independence.