Danish police have hinted Russia may have been behind a swarm of drones that shut down Copenhagen airport, disrupting around 100 flights and leaving 20,000 passengers stranded as authorities issue a chilling warning of sabotage.

Police inspector Jens Jespersen suggested that the incident had all the signs of a sophisticated operation.

He said: 'The number, size, flight patterns, time over the airport. All this together indicates that it is a capable actor. Which capable actor, I do not know.'

In further hints that they believe Vladimir Putin was behind the drones, authorities said that the perpetrator was seeking to demonstrate certain abilities.

Ukrainian president Volodymyr Zelensky, in a social media post, referred to 'Russia's violation' of NATO airspace in Copenhagen. However, he did not indicate the source of his claim.