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COPENHAGEN, Denmark (AP) — A bomb threat against a natural gas processing facility in central Norway forced the site’s evacuation and briefly halted operations, police said Thursday, adding later that the threat wasn’t credible.

The incident came amid heighten security on key energy, internet and power infrastructures following last month’s underwater explosions that ruptured two natural gas pipelines in the Baltic Sea that were built to deliver Russian gas to Germany.

The blasts and ruptures happened in international waters off the Baltic coastline of both Sweden and Denmark but within the countries’ exclusive economic zone. The damaged Nord Stream pipelines discharged huge amounts of methane, a potent greenhouse gas, into the air.

Gas from Norway’s Ormen Lange deepwater facility off the coast — which supplies around 20% of UK’s gas needs — is piped along the seabed to the onshore Nyhamna facility, which was evacuated. The gas is then exported to the U.K.

Police said there was ”no evidence that the bomb threat against the Ormen Lange facility was real.”

“The perpetrator is known to the police for similar circumstances and the case is being investigated further,” said police spokesman Per Åge Ferstad.

Norwegian broadcaster NRK later said a man, known for having made similar threats over several years, had been detained. NRK added that ma,n who was not identified, previously had been convicted in several similar cases.

Nyhamna is 375 kilometers (233 miles) northwest of Oslo. It is Norway’s second-largest gas field and is operated by the Norwegian branch of Shell.

Shell later told Norwegian news agency NTB that workers had returned to the site and production had resumed.