Officials in Kyiv and Berlin condemned Russian President Vladimir Putin’s announcement that Moscow would station tactical nuclear weapons in neighboring Belarus.

The Kremlin “took Belarus as a nuclear hostage,” Oleksiy Danilov, the secretary of Ukraine’s National Security and Defense Council, tweeted on Sunday.

Mykhailo Podolyak, an adviser to Ukrainian President Volodymyr Zelenskyy’s office, added that the move was a violation of the nuclear non-proliferation treaty, something that Putin denied in his announcement on Saturday. Podolyak tweeted that Putin “is afraid of losing & all he can do is scare [us] with tactics.”

Putin said on Saturday that Russia would construct a storage facility for tactical nuclear weapons in Belarus by July. He likened the plans to the U.S. stationing its nuclear weapons in Europe, and said Russia would retain control of the nuclear arms stationed in Belarus.

“The United States has been doing this for decades,” Putin was quoted as saying. “They deployed their tactical nuclear weapons long ago on the territories of their allies, NATO countries, in Europe,” he said.

Saturday evening, the German Federal Foreign Office told national media that the decision was akin to a “further attempt at nuclear intimidation.”

“The comparison made by President Putin on the nuclear participation of NATO is misleading and cannot serve to justify the step announced by Russia,” the Foreign Office was quoted as saying.