Several US government agencies are warning that unidentified hackers are trying to breach Siemens devices that monitor and operate water facilities and other critical infrastructure systems, Reuters reports citing a cybersecurity advisory.

The warning comes amid widespread cyber incidents targeting local water systems in multiple states in recent weeks in attacks cybersecurity experts suspect are linked to Iran.

The advisory describes an “active threat” to all Siemens S7 Series programmable logic controllers across multiple critical infrastructure sectors, including manufacturing, energy, water and wastewater, chemical, food and agriculture facilities, according to the warning issued by the National Security Agency, the FBI, Department of Energy, Environmental Protection Agency and the Department of Homeland Security’s Cybersecurity and Infrastructure Security Agency.

Siemens has not immediately responded to a request for comment.