Fighting has intensified near a nuclear power plant in Ukraine that is Europe’s largest, further increasing the possibility of a war-related nuclear accident, the head of the International Atomic Energy Agency said on Tuesday.

“There is an increased level of combat, active combat” in the area of the Zaporizhzhia Nuclear Power Plant, IAEA director general Rafael Mariano, Grossi told The Associated Press in an interview. “My teams there report daily about the attacks, the sound of heavy weaponry. This is practically constant.”

Speaking a day before he was to cross the front lines for a second time to visit the plant, Grossi said he felt it was his duty to ramp up talks aimed at safeguarding the facility.

He met on Monday with Ukrainian President Volodymyr Zelensky and said he would probably head to Russia in the coming days.

Grossi has long called for a protection zone to be set up around the plant, which is very near the front line of the war. But so far, an agreement has been elusive.

“It is a zone of extreme volatility. So the negotiations are, of course, affected by the ongoing military operations,” Grossi said. “I would not characterise the process for the last few months as one that has not led to any progress.”

The UN’s atomic energy watchdog, which is based in Vienna has a rotating team permanently based at the plant. The station’s 6 reactors are in shutdown and the plant has received the electricity it needs to prevent a reactor meltdown through one remaining power line.

Plant personnel have had to switch to emergency diesel generators several times during the 13-month war to power essential cooling systems.

Military analysts expect the fighting between invading Russian troops and Ukrainian forces will further escalate as spring progresses and the ground hardens, allowing heavy military machinery to advance on the battlefield.

“There is talk about offensives, counter-offensives,” Grossi said. “The concentration of troops, concentration of military equipment, heavy weaponry has grown exponentially in the area near to the plant, which of course, makes us believe that the possibility of an accident, of a renewed attack ... could grow.”