The core of a nuclear research facility in the besieged city of Kharkiv in Ukraine is still intact, despite heavy shelling by Russian forces on Thursday.

“The facility, in working condition, doesn’t present any danger whatsoever,” Mykola Shulga, director general of the National Science Centre Kharkiv Institute of Physics and Technology, told Reuters on Friday.

News of no damage to the core of the facility that houses nuclear fuel will come as a relief to facility staff as well as residents of Kharkiv as a fire had reportedly broken out near the research centre in the aftermath of Russian shelling on Thursday.

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However, Shulga told Reuters that while the facility was fine as of now, further damage could cause a catastrophe.

“However, if there is physical damage, a nuclear fuel leak is possible, radioactive elements (could escape) outside. This obviously would be a huge, huge problem for the environment. In other words, what would happen would be comparable to a similar situation at any nuclear power station,” the director general said in a dire warning.

Earlier in the day, Ukrainian intelligence issued a similar warning and accused Russia of plotting a “terrorist attack” on the captured Chernobyl nuclear facility to pin the blame of the resulting disaster on Kyiv. Ukrainian foreign minister Dymtro Kuleba also warned that Russian mismanagement of the plant could spell disaster and lead to radiation leaks.

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Since the Russian invasion of Ukraine began on February 24, Russian forces have moved swiftly to capture several nuclear facilities, including the defunct Chernobyl plant and the Zaporizhzhia nuclear power plant, which happens to be Europe’s largest.

While both sites are under Russian control, Ukrainian staff are managing operations in conditions that UN nuclear watchdog IAEA says could put the nuclear facilities at risk and create a disaster.