"Putin wants to go as far as we allow him - not only Ukraine, but the whole of Europe," Poroshenko said in an interview with French radio station RFI.
"If you had asked me two years ago, I would have said this was impossible because the whole postwar security system would not allow that," he said." But if you asked me today... unfortunately everything is possible because the annexation of Crimea and the eastern part of Ukraine... shows we can break the global security system."
He said the ongoing fighting against Russian-backed insurgents in eastern Ukraine should be seen as a fight for entire Europe.
"Is an attack on Finland possible? Yes, and Finland knows that. Is an attack on the Baltic states possible? Yes," he said.
"When we are talking about the fighting in the east of my country... we are fighting not only for the independence and sovereignty of my country, we're fighting for democracy, we are fighting for freedom and the security of the whole European continent."
On 27 May Lithuanian government has allowed renewing more flights to Germany and the Netherlands .