Environmental activists invaded the runways of four German airports on Thursday, causing temporary flight cancellations at some of them, the latest in a series of similar protests.

A statement from the campaign group Last Generation said eight activists took part in coordinated protests at Berlin, Cologne/Bonn, Nuremberg and Stuttgart airports, demanding that the German government negotiate and commit to a global phase-out of oil, gas and coal production by 2030.

The German news agency dpa reported that flight traffic was temporarily suspended at Nuremberg and Cologne/Bonn airports after demonstrators were glued to the ground. At Berlin Brandenburg Airport, two activists were taken away and arrested.

Nuremberg Airport reported on social media that disruptions by activists led to a brief suspension of air traffic lasting over an hour, resulting in six delays, one cancellation and one flight diversion.

Cologne/Bonn Airport temporarily suspended operations due to a security breach: police reported that intruders had cut a hole in the outer fence.

Stuttgart Airport said air traffic remained unaffected after police promptly arrested two demonstrators who tried to block a taxiway.

Reuters reported that Last Generation had previously announced its plans for disruptive actions in several countries in Europe and North America.

Founded in 2021, the group owes its name to activists who see themselves as the last generation before climate collapse.

“Billions of human lives are at stake,” one of the group’s activists said in a video from an airfield shared on social media on Thursday. “Climate collapse is already a reality for many people. We still have the privilege of being able to do something about it here.”

German Interior Minister Nancy Faeser condemned the protests on the social network X.

“These criminal actions are dangerous and stupid,” she wrote, warning that the activists “are not only risking their own lives, but also endangering the lives of others.”

German politicians have been calling for increased airport security since violations by climate activists brought air traffic to a standstill. Last month, for example, there were disruptions on two consecutive days at Frankfurt Airport, the country’s busiest airport.

Faeser referred to the bill recently passed by the German cabinet, which provides for tougher penalties for violations of security checks at airports.

The bill, which still needs parliamentary approval, would impose prison sentences of up to two years for people who intentionally enter restricted areas such as taxiways or runways, pose a threat to civil aviation or facilitate such acts by others. This would be a change from the current system, where such trespassing is usually only punishable by fines.