Censor.NET reports citing Deutsche Welle.
Many European countries have slashed defense spending since the 2008 financial crisis. That has raised concern in the United States and NATO about Europe's declining military capabilities, especially at a time of heightened tension with Russia over Ukraine.
NATO chief Jens Stoltenberg joined the 28 EU leaders to talk about "the new threats facing Europe at a time of hybrid warfare, global terrorism and cyber attacks," Tusk said.
Stoltenberg's presence symbolized how NATO and the EU are working more closely together to counter so-called "hybrid" warfare.
The term covers unconventional techniques such as Russia's use of soldiers without military insignia in Crimea, as well as cyber attacks, economic pressure, propaganda and the use of social media by Islamist militants to recruit supporters.
As part of the work, the EU is studying how to counter what it says is deliberate misinformation coordinated by the Kremlin over Moscow's role and aims in Ukraine and elsewhere in Europe. Russia denies sending soldiers and weapons to fan the separatist conflict in its former Soviet neighbour.
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