US officials suspect Iranian hackers may be behind a series of breaches targeting systems that monitor fuel levels in storage tanks serving gas stations across multiple US states, according to multiple sources briefed on the activity, The Caspian Post reports, citing CNN.

The hackers are believed to have exploited automatic tank gauge (ATG) systems that were connected online and left unprotected by passwords. This allowed them in some cases to manipulate display readings on the tanks, although not the actual fuel levels themselves, the sources said.

While the cyber intrusions are not known to have caused any physical damage or injuries, they have raised safety concerns. Experts and US officials warned that gaining access to an ATG system could, in theory, enable a hacker to conceal a gas leak, potentially preventing it from being detected.

Sources familiar with the investigation said Iran’s past pattern of targeting fuel infrastructure systems is one reason it is considered a leading suspect. However, they also cautioned that US authorities may not be able to definitively attribute the breaches due to limited forensic evidence left behind by the attackers.

If Iran’s involvement is confirmed, it would be the latest case of Tehran threatening critical infrastructure in the US homeland, which remains out of reach of Iranian drones and missiles, amid the US and Israeli war with Iran.

It could also raise a politically sensitive issue for the Trump administration by drawing further attention to higher gas prices caused by the war. Seventy-five percent of US adults surveyed in a recent CNN poll said the Iran war had a negative effect on their finances.

The hacking campaign is also a warning to many US critical infrastructure operators who have struggled to secure their systems despite years of federal exhortations.