Norwegian police revealed on Oct. 17 that they had arrested four Russians on suspicion of illegally photographing classified facilities last week, days before they caught two other Russians allegedly in possession of drones.

Norway has ramped up security in recent weeks following a number of drone sightings close to its oil and gas infrastructure and in response to the Sept. 26 leaks on the Nord Stream gas pipelines off the costs of Sweden and Denmark.

“We’re seeing the consequences of the new security situation in Norway,” Justice Minister Emilie Enger Mehl told a news conference. “We can’t rule out further cases.”

Police said last week they had arrested a Russian-Israeli man an at-border checkpoint with drones in his car on Oct. 13, and another Russian found flying a drone and in possession of cameras at an airport in the Arctic town of Tromsoe on Oct. 14.

A statement from Nordland county police on Oct. 17 revealed the earlier arrests of three men and one woman on Oct. 11. It said cameras and extensive photographic material had been seized from their car, but no drones were found.

A court on Oct. 14 gave police permission to hold the four suspects in custody for one week.