Rafael Mariano Grossi, the International Atomic Energy Agency's director general,  called strikes at Zaporizhzhia nuclear power plant "alarming."
CNN  — 

Ukraine accused Russian forces on Sunday of launching rockets at the Zaporizhzhia nuclear power plant, further ratcheting fears of an accident a day after the United Nation’s watchdog warned that fighting at the occupied complex risked a “nuclear disaster.”

It was the second time in as many days that the plant, which is the largest of its kind in Europe, was hit. Ukraine and Russia have traded blame for both attacks.

The rockets launched on Saturday night struck near a dry storage facility, where 174 casks with spent nuclear fuel are kept, according to Energoatom, Ukraine’s state-run nuclear power company. Explosions blew out windows in parts of the plant and one worker was hospitalized with shrapnel wounds.

“Apparently, they aimed specifically at the containers with processed fuel, which are stored outside next to the site of shelling,” the company said in a statement on Telegram.

Three radiation monitoring detectors were also damaged on Saturday, making “timely detection and response in case of aggravation of the radiation situation or leakage of radiation from spent nuclear fuel casks are currently impossible,” Energoatom said.

“This time a nuclear catastrophe was miraculously avoided, but miracles cannot last forever,” it added.

The Zaporizhzhia nuclear power plant is seen from afar on Thursday.

Kyiv has accused Russian forces of storing heavy weaponry in and launching attacks from the plant, which they took over in early March and still occupy. Moscow, meanwhile, has claimed Ukrainian troops are targeting the complex.

The head of the pro-Russian regional administration in Zaporizhzhia, Yevgeny Balitsky, said in a statement on Telegram Sunday that Ukrainian forces had targeted the spent fuel storage area and damaged administrative buildings.

Fears about the security of Zaporizhzhia nuclear plant have been growing since Russian forces seized the site, but reached an inflection point on Friday when shelling damaged a high-voltage power line and forced one of the plant’s reactors to stop operating – despite no radioactive leak being detected.

After the attack, Energoatom said that Russian shellfire had damaged a nitrogen-oxygen station and the combined auxiliary building, and that there were “still risks of hydrogen leakage and sputtering of radioactive substances, and the fire hazard is also high.”

The director general of the International Atomic Energy Agency (IAEA), Rafael Mariano Grossi, said he was alarmed by the reports of damage and demanded that an IAEA team of experts urgently be allowed to visit the plant, to assess and safeguard the complex.

“I’m extremely concerned by the shelling yesterday at Europe’s largest nuclear power plant, which underlines the very real risk of a nuclear disaster that could threaten public health and the environment in Ukraine and beyond,” Grossi said in a statement Saturday.

“Military action jeopardizing the safety and security of the Zaporizhzya nuclear power plant is completely unacceptable and must be avoided at all costs,” he added.

Ukrainian President Volodymyr Zelensky, who has accused Russia of using Zaporizhzhia nuclear power plant to wreak terror in Europe, said Sunday that he spoke with European Council President Charles Michel about the situation at the complex.

“Russian nuclear terror requires a stronger response from the international community - sanctions on the Russian nuclear industry and nuclear fuel,” Zelensky tweeted.

CNN was unable to verify claims of damage at the plant, which lies on the banks of Dnipro River. Ukrainian prosecutors have opened an investigation into the shelling.

‘Irresponsible breach of nuclear safety rules’

The European Union’s top diplomat has slammed Russia’s military activities around the Zaporizhzya power plant and called for the IAEA to gain access to the complex.

“This is a serious and irresponsible breach of nuclear safety rules and another example of Russia’s disregard for international norms,” Josep Borrell, the EU’s foreign policy chief, said Saturday on Twitter.

Several Western and Ukrainian officials believe that Russia is now using the giant nuclear facility as a stronghold to shield their troops and mount attacks, because they assume Kyiv will not return fire and risk a crisis.

US Secretary of State Antony Blinken has accused Moscow of using the plant to shield its forces, while Britain’s ministry of defense said in a recent security assessment that Russia’s actions at the complex sabotage the safety of its operations.

The Ukrainian mayor of Enerhodar, Dmytro Orlov, said in late July that Russian forces had been observed using heavy weaponry near the plant because “they know very well that the Ukrainian Armed Forces will not respond to these attacks, as they can damage the nuclear power plant.”

Ukraine’s foreign ministry warned on Friday that further attacks on the plant could be disastrous.

“The possible consequences of hitting an operating reactor are equivalent to the use of an atomic bomb,” the ministry said on Twitter.

Grossi has called for all parties to “exercise the utmost restraint in the vicinity of this important nuclear facility, with its six reactors.”

While the security situation is stable and there is no immediate threat to nuclear safety, according to the IAEA, Grossi warned of the dire risk that further fighting at the site could pose.

“Any military firepower directed at or from the facility would amount to playing with fire, with potentially catastrophic consequences,” Grossi said.

The IAEA has been trying to coordinate a mission of safeguarding experts to visit the plant since it was seized by Russian forces.

“This mission would play a crucial role in helping to stabilise the nuclear safety and security situation there, as we have at the Chernobyl nuclear power plant and elsewhere in Ukraine in recent months,” he said.

The IAEA sent teams to Chernobyl nuclear power plant in late April and in May to deliver equipment and conduct radiological assessments of the site, which was held by Russian forces for more than a month before they withdrew in late March.

CNN’s Mariya Knight, Vasco Cotovio and Tim Lister contributed to this report.