"We need a long perspective strategy... plans for years. We need to be realistic, we have to treat this as a long-term game," Tusk said after chairing his first European Union leaders summit, which reviewed relations with Russia.

"We must go beyond being reactive and defensive," he said, calling on Europeans to "regain our self-confidence and realise our own strength" when dealing with Russia.

Russia's intervention in Ukraine and especially its annexation of Crimea in March has sparked the worst crisis in
Europe since the end of the Cold War.

It has also badly exposed differences within the EU over how best to respond.

Some member states such as Germany and Italy with major trade and political ties to Russia have been reluctant to take too hard a line and only came round slowly to imposing sanctions against Moscow.

Others such as Britain pressed for tough sanctions from the start, stressing the need to send a strong message to Russian President Vladimir Putin that the West would not accept a fait accompli in Ukraine and Crimea.

Tusk is the first East European to head the European Council of EU leaders and in his previous role as Polish prime minister advocated a similarly tough response.

On Thursday, he said Russia posed a major challenge for the EU but that the summit discussion had been pragmatic and practical.

"The EU needs a common, united position," he said, adding it was "absolutely clear that all EU states want to be together (in facing) the challenge on our eastern borders."

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