The International Atomic Energy Agency is placing groups of experts at all four of Ukraine’s nuclear power plants to reduce the chances of severe accidents as Russia’s invasion continues, agency director Rafael Grossi said Wednesday.

The United Nations body already has a presence at the Zaporizhzhia nuclear power plant — the largest in both Ukraine and Europe — which has been held by Russian forces since early in the war.

The IAEA’s permanent presence at all four of Ukraine’s nuclear stations, with at least 11 staff in total, marks an unprecedented expansion for the agency. IAEA technicians will also be at Chernobyl, the now-closed nuclear plant that was the site of the 1986 nuclear disaster that spread fallout over much of Europe.

In the latest incident highlighting the nuclear safety and security risks in Ukraine, the South Ukraine, Rivne and Khmelnitsky NPPs reduced their power output during the weekend while the country’s energy infrastructure was under missile attack. The levels have since been restored.

Ukraine also reported that missile attacks on Kyiv caused a fire in a warehouse on the site of the Kyiv Research Institute. The site holds a defueled research reactor, the core of which is stored in a spent fuel storage facility on the site. No personnel were injured. Radiation monitoring was performed and no changes were measured.

“From tomorrow, there will be two flags at all of the nuclear facilities in Ukraine; one of Ukraine and the second of the international nuclear agency,” Ukraine’s Prime Minister Denys Shmyhal said at a joint press conference with Grossi at the government headquarters in Kyiv on Wednesday.

Grossi arrived in Ukraine this week to raise the IAEA flag and install staff at each nuclear facility, visiting Chernobyl on Wednesday and Rivne Tuesday. Staff will remain at the facility for “as long as they are requested” by the Ukrainian government, he said.

The IAEA flags flying in Ukraine are “not just symbolic” said Grossi. “They reflect and they will signify the presence of some of the best-renowned experts in safety and security who will provide advice, and technical support during this very difficult time to each facility facing different challenges and problems depending on the situation.”

Shmyhal also said he requested the IAEA to impose sanctions on Rosatom, Russia’s state nuclear corporation, and deprive Moscow of rights and privileges within the IAEA, as well as to halt any form of nuclear co-operation with the country. Grossi said that decision would fall on member states to discuss.

Grossi said that the IAEA experts — who are present at Ukraine’s request — will deepen the technical expertise at each plant to prevent nuclear accidents as Russia’s war, now in its 11th month, continues, as well as monitor nuclear safety and security systems.

“Quite simply there are attacks on (the plants),” Shmyhal said. “We want to avoid any nuclear accidents, therefore we turned to the IAEA for security and protection.”

The Zaporizhzhia nuclear power plant in southeastern Ukrain  is located on the frontline of ongoing battles between Ukrainian and Russian forces. Russian forces captured the facility in March, and it has repeatedly come under fire since. All six reactors there are now shut down, though the plant is still connected to the electricity grid for safety reasons.

Grossi is pressing to establish a nuclear safety and security protection zone around Zaporizhzhia, where the IAEA has been present for more than four months.

“I remain determined to make the much-needed protection zone a reality as soon as possible. My consultations with Ukraine and Russia are making progress, albeit not as fast as they should,” Grossi said in an earlier statement on Tuesday.

At the press conference he said the IAEA was still in consultation with the Ukrainian government about establishing the zone. “We are closer to a good outcome,” he said.

Staff at Zaporizhzhia are also being urged to sign contracts with Rosatom, while the national Ukrainian operator Energoatom is urging them not to do so, the IAEA said, adding that their inspectors at the plant have nonetheless reported that “despite all the challenges, the plant still has adequate operational staff to maintain the safe operation of all units at the plant’s current level of functioning.”