Polish authorities are assuming a leak in a pipeline bringing Russian oil to Europe is probably an accident.

Investigations continue, but Mateusz Berger, Poland’s top official in charge of strategic energy infrastructure, said he has no reason to think it was an act of sabotage.

“I prefer to assume it was probably an accident,” Berger said. “It’s not the first case of leakage and it surely can’t be compared to the explosion on Nord Stream.”

European authorities are on high alert for any attacks on infrastructure since the explosions on the Nord Stream gas pipelines in September. German train services were also disrupted earlier this month by what the government called an act of sabotage. NATO ministers are meeting this week, with the protection of energy assets on the agenda.

Polish pipeline operator PERN said earlier on Wednesday that it expects to know the potential causes of the leak on the Druzhba pipeline within a few hours. The issue was discovered late on Tuesday about 70 kilometers (44 miles) to the west of Plock, Poland, where PKN Orlen SA’s biggest refinery is located.

The incident has affected one of two strands of the northern leg of the Druzhba network, which supplies Germany and Poland. The other line is still operational and delivering crude to the PKN Orlen refinery. Crude can also be pumped from Poland’s Baltic Sea terminal to Germany along a separate route.

“Security of supply in Germany is currently guaranteed,” said a spokeswoman of the country’s Economy Ministry. “The two refineries, Schwedt and Leuna, currently continue to receive crude oil.”

Druzhba delivers crude to Germany’s key Schwedt refinery, which the government nationalized from its Russian stakeholders last month as part of efforts to sever decades of tight energy ties with Moscow. It is preparing to stop receiving oil from the country later this year. 

Crude prices were up slightly on the news as traders watched for any signs pointing to potential sabotage. Brent crude rose 0.5% to $94.78 a barrel as of 11:18 a.m. in London. 

European governments are racing to bolster security, with EU Commission President Ursula von der Leyen saying explicitly that energy assets have become a target amid Russia’s war against Ukraine. Defense ministers of the NATO military alliance are starting a two-day meeting in Brussels on Wednesday, with Secretary-General Jens Stoltenberg saying the group will further step up the “protection of our critical infrastructure.”

The southern leg of Druzhba, which isn’t affected by the leak, delivers oil toward Hungary, Slovakia and the Czech Republic. Flows are set to continue along that part even after EU sanctions kick in, after Hungary and others lobbied for an exemption.