Russian hackers have reportedly targeted three nuclear research laboratories in the US. A group called Cold River carried out a phishing campaign against scientists at the Brookhaven, Argonne and Lawrence Livermore national laboratories last summer in an attempt to obtain passwords, Reuters reports.

The efforts are believed to have taken place in August and September, around the time UN experts visited a nuclear power plant in Russia-controlled Ukrainian territory to help prevent a potential disaster following heavy shelling in the area. Meanwhile, President Vladimir Putin has alluded to a readiness to defend Russia-claimed territory with nuclear weapons.

It’s not clear whether the phishing attempts were successful or why the hackers were trying to gain access to the labs’ systems. However, Adam Meyers, senior vice president of intelligence at cybersecurity firm CrowdStrike, told Reuters that Cold River is “involved in directly supporting Kremlin information operations.”

Last year, the group leaked emails from the former chief of MI6, the UK’s foreign intelligence service. Cold River is also said to have targeted non-government organizations investigating war crimes. It reportedly conducted such a campaign around the time a UN commission said that Russian forces were responsible for war crimes and human rights violations in the early days of the country’s invasion of Ukraine.