Germany's Cologne-Bonn airport suspended flights for several hours on Wednesday after climate activists glued themselves to a runway, while similar actions at other European airports were foiled by authorities.
Cologne-Bonn airport, Germany's sixth-largest, said it had resumed operations during the morning after halting all flights shortly before 6 a.m. (0400 GMT).
The campaign group Last Generation said on X that it had blocked air traffic at the airport, and published pictures of several activists with their hands glued to the runway.
The group, which wants the German government to pursue a global agreement to exit oil, gas, and coal by 2030, listed several countries across Europe and North America where similar airport disruptions were planned on Wednesday.
Authorities said separately that activists' attempts to disrupt airports in London, Vienna, Oslo, and Zurich had been foiled, and no major air traffic delays were reported there.
However, Last Generation activist Ronja Kuenkler told media after the Cologne protest: "Today was just the beginning. Over the next few weeks we'll repeat this in Germany, Europe and around the world."
She declined to say whether the Paris Olympics, starting on Friday, could be targeted.
British police said in a post on X they had arrested nine members of the climate action group Just Stop Oil for conspiring to disrupt Heathrow Airport, one of the world's busiest.
In Switzerland, three anti-oil demonstrators were detained after blocking a road to Zurich airport, police said. Footage broadcast on Swiss media showed a man gluing his hand to the road, sitting beside two other protesters holding banners.
Vienna airport said four protesters had spilled paint in a check-in area but police had intervened quickly to prevent further disruption.
In Norway, three activists were apprehended after cutting a hole in a fence and briefly making it onto a runway at Oslo Airport, police said.
Helsinki's Vantaa airport said a demonstration by climate activists had had no impact on passengers or operations.
(Reporting by Ludwig Burger and Klaus Lauer; Additional reporting by Terje Solsvik in Oslo, Sachin Ravikumar in London and Dave Graham in Zurich, Francois Murphy in Vienna, Louise Breusch Rasmussen in Copenhagen; Editing by Miranda Murray, Alex Richardson, Bernadette Baum and Kevin Liffey)