Ukrainian President Volodymyr Zelensky. Ukrainian President Volodymyr Zelensky speaks during "Summit of the Future" on the sidelines of the UN General Assembly at the United Nations Headquarters in New York, September 23, 2024. He warned of the nuclear threat that Russia poses in its full-scale invasion of Ukraine. Photo: Timothy A. Clary/Getty Images

In addressing the U.N. General Assembly, Zelensky warned that, if Vladimir Putin was prepared to resort to such a move, "it means nothing you value matters to Moscow."

Newsweek has contacted the Kremlin by email for comment on the claims. The Ukrainian president did not specify which plants were under threat, but there are three operating nuclear power plants on Ukrainian-held territory.

These are located in Rivne and Khmelnytskyi in the west and Pivdennoukrainsk in the south of the country. The Zaporizhzhia Nuclear Power Plant, Europe's largest, has been under Russian control since March 2022 and is disconnected from Ukraine's power grid, but its location in the middle of hostilities has sparked global concern.

Since the start of Putin's full-scale invasion, the threat that the war in Ukraine could have a nuclear dimension has been expressed variously through threats by Kremlin propagandists and Moscow's statements of its weapons capabilities.

Ukrainian Foreign Minister Andrii Sybiha said on September 21 that possible targets for Russian forces included open distribution devices and transmission substations, which are crucial for the safe operation of nuclear infrastructure.

Separately, Zelensky had told ABC News that Russia was using Chinese satellites to photograph Ukraine's nuclear sites, and added that "there is a threat of strikes against the nuclear objects." During his address to the U.N., Zelensky said that "this kind of Russian cynicism will keep striking if it's given any room in the world," adding that the U.N. Charter "leaves no room for that and that's why the Peace Formula leaves no room either."

Zelensky called on U.N. countries to support a second peace summit "to end the war" following the first event in June in which Russia did not attend. Zelensky is in the U.S. to tout his "victory plan," which he has not clarified publicly but will present to President Joe Biden, U.S. Congress, and presidential contenders Kamala Harris and Donald Trump.

Anatol Lieven is director of the Eurasia Program at the Quincy Institute for Responsible Statecraft think tank based in Washington, D.C. He told Newsweek that, for Zelensky, victory is defined as the withdrawal of Moscow's forces from all the Ukrainian territory they now occupy.

"There is nothing in the existing, or feasible, balance of forces and resources between Ukraine and Russia to suggest that this is possible, even should greatly increased Western aid be forthcoming," Lieven said.

However, Kyiv's incursion into Russia's Kursk region showed that Ukraine was capable of counterattacks, and the territory it has captured was "a potential bargaining chip in future negotiations, not a harbinger of Ukrainian victory."