Russia: "You have crossed the red line"

What nuclear safety regulations specifically involve the red line referred to by Russia?

Russian Foreign Ministry spokesperson Zakharova made a statement on the 28th, condemning the targeted strikes on the heavy water reactor in the Central Province of Iran and the uranium enrichment facility in Yazd Province on the 27th, as well as the subsequent shelling of the Bushehr nuclear power plant area. She stated that these attacks should be clearly and firmly condemned by the international community.

Zakharova urged the leadership of the International Atomic Energy Agency to make a clear statement, conveying to the aggressors the signal that “you need to stop, you have crossed the red line.” She pointed out that attacking civilian nuclear facilities openly violates the Treaty on the Non-Proliferation of Nuclear Weapons, the verification mechanisms of the International Atomic Energy Agency, and relevant regulations in the field of nuclear and physical safety. The Russian side firmly condemns this destructive policy, and the attackers must stop immediately.

(Source: CCTV News)