COPENHAGEN, Denmark (AP) — Europe is in the middle of a hybrid war waged by Russia and the continent must arm itself, Danish Prime Minister Mette Frederiksen warned on Wednesday as she hosted a summit of European Union leaders in Copenhagen.

“I hope that everybody recognizes now that there is a hybrid war and one day it’s Poland, the other day it’s Denmark, and next week it will probably be somewhere else that we see sabotage or we see drones flying,” Frederiksen told reporters.

Wednesday’s summit comes after a spate of troubling drone incidents at Danish airports and military bases over the last week. Ahead of the meeting, a special radar system was set up at Copenhagen airport to help keep watch. Unidentified drones forced the closure of the airfield a week ago, causing major disruptions.

France, Germany, the Netherlands, Sweden and the U.K. also sent aircraft, ships and air defense systems to Denmark ahead of the talks. Ukraine’s armed forces have dispatched a mission to the Nordic country for joint exercises, sharing its expertise on combating Russian drones.

While the Danish authorities have not identified those believed to be responsible, Frederiksen said, “There is only one country that are willing to threaten us and it is Russia and therefore we need a very strong answer back.”