Russian military forces have been enhancing defensive positions in and around the Zaporizhzhia nuclear power plant in southern Ukraine in recent weeks, four witnesses said, ahead of an expected counteroffensive in the region.
New trenches have been dug around the city and more mines have been laid. Surveillance cameras at the plant are pointing north across a wide reservoir towards Ukrainian-controlled territory.
The Russians have had firing positions set up atop some of the plant's buildings for several months. Nets have been erected as a possible deterrent to drones.
The measures described by two Ukrainians who work at the power plant and two other residents in the city of Enerhodar underline the risks the war poses to the security of the facility.
The sources spoke on condition of anonymity because of fears for their safety in a city under Russian occupation.
Rosatom: Military action by Ukraine poses a threat to nuclear safety
Russian state nuclear energy company Rosatom said any possible military action by Ukraine posed a threat to nuclear safety, and that the plant's equipment was being maintained properly. The Ukrainian military intelligence agency and the Russian defense ministry did not respond to requests for comment.
Some nuclear industry experts said they were alarmed and warned that any damage to the plant could have dire consequences for people, the surrounding area, the war and the global nuclear industry.
"Nuclear reactors were not designed for war zones and I do not believe they can be safe or secure in a war zone," said Nickolas Roth, director at think tank the Nuclear Threat Initiative.
Petro Kotin, chief of Ukraine's Energoatom nuclear agency, told Reuters he did not believe Ukrainian forces would stage an attack directly on the site and could instead try to force the Russians to retreat by cutting off supply lines.
But there is a concern in the international community that the six-reactor nuclear plant, Europe's largest, could be caught up in the fighting, particularly as military analysts expect Ukraine to try to push Russian forces back in the Zaporizhzhia region.
The UN nuclear watchdog says that the military presence and activity are growing in the region, underlining the need for urgent action. It has warned for months of the danger of a major accident at the plant.
The agency plans to present a deal between Russia and Ukraine to the UN Security Council later this month to protect the facility, four diplomats told Reuters.