The airports of Copenhagen and Oslo reopened today after being closed yesterday, Monday, due to the presence of unidentified drones, police and airports said.

In Copenhagen, “the drones have disappeared and the airport is open again,” police official Jakob Hansen said.

Danish police also said today that the drones, which caused the country’s main airport to close yesterday, appeared to have been operated by “a competent pilot”, adding that no suspects had been identified.

“We concluded that it was someone we would call a competent operator,” police chief Jens Jespersen told reporters today about the drones seen in Copenhagen.

“It is someone who has the skills, the will and the tools to demonstrate in this way,” Jespersen said, adding that it is still too early to tell whether the incidents in Denmark and Norway are connected.

Copenhagen Airport was closed for four hours after two or three large drones were spotted flying too close, officials said. Meanwhile, Oslo Airport was closed for three hours after two drones were observed, according to local police. The Norwegian capital’s airport reopened today at 03:15 (local time, 04:15 GMT).

Jespersen said the drones in Denmark came from different directions, flashing their lights before disappearing after hours.

Flights were redirected to other airports and problems with air travel are expected today until traffic is restored, the two airports said.

Danish and Norwegian authorities are working together on these incidents, police official Jakob Hansen stressed, clarifying that the military and intelligence services have been mobilized.

The origin of the drones, which disappeared without being intercepted, has not been known so far, Hansen admitted.”At this stage, we do not know” whether these aircraft may be of Russian origin, he clarified when asked about it.