Human Rights Watch (HRW) on Monday reported that Israeli strikes on four Iranian oil depots put the health of civilians and the environment at risk and may constitute war crimes under international humanitarian law.

The group warned that the release of toxic pollutants may impose long-term effects on man-made and natural environments. HRW alerted to potential contamination and acidification of waterways and soil and increased risks of chronic respiratory and cardiovascular disease.

Israeli forces said the attack complied with international humanitarian law and claimed the strikes were limited to military objectives to disrupt Iranian army fuel supply lines. However, HRW later claimed that targeted depots were used for civilian purposes.

Israeli forces launched attacks on the oil depots surrounding Tehran on March 7, straining the country’s energy infrastructure and producing “black rain” from the release of toxic pollutants into the air. Iranians continue to face negative effects from pollution caused by the conflict.

After the attack–which came amidst a series of fights between Iran, Israel, and the US–the UN Environmental Program said the severity of environmental consequences from the conflict should trigger an immediate cessation of hostilities.

To prevent environmental harm, international humanitarian law mandates that countries engaged in armed conflict must follow certain principles to minimize civilian and environmental destruction, whether incidental or intentional.

Armed conflict rules include principles of distinction, precaution, and proportionality, which create protections for civilian property and populations. Distinction mandates that civilian property, including the natural environment, may not be attacked unless it is a military objective, while proportionality and precaution require that retaliatory military force must be proportional and feasible measures should be taken to minimize damage to humans and the environment.

Additionally, the laws of armed conflict under international law consider military objectives unlawful if they cause widespread, long-term, and severe damage to the natural environment. The principle is generally considered difficult to violate, as “widespread” and “severe” are high thresholds, and “long-term” only encompasses damage that lasts decades.

In order for such military force to be considered a war crime, HRW said national and military actors must demonstrate criminal intent. The group contended that Israel’s failure to account for the foreseeable, long-term environmental harm inflicted upon the area surrounding Tehran may establish such intent.