Danish premier Mette Frederiksen on Wednesday urged Europe to step up its response to Russia's "hybrid war", as she hosted EU leaders for defence talks held under tight security following mystery drone flights.

Thousands of police were on alert, civilian drones banned and reinforcements deployed from NATO allies to help protect the summit at the grand Christiansborg Palace in Copenhagen.

"I hope that everybody recognises now that there is a hybrid war," Frederiksen said.

Denmark -- which holds the EU's rotating presidency -- has been rattled in recent days as unidentified drones shut down airports and flew near military sites.

Suspicions have pointed at Russia -- but so far no culprit has been definitively named.

Nonetheless the drone incidents have sharpened the focus on chinks in Eu

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