Russia appears to be ramping up threats of a nuclear war. On Tuesday, a Russian diplomat told the United Nations that while the Ukraine invasion does not warrant the use of nuclear weapons, Russia could resort to nukes in response to “direct aggression” from the West. The comments came just one day after Ukraine asked the U.N. to declare their country a nuclear weapon-free zone.

“The robust joint actions are needed to prevent nuclear disaster,” said Mykola Tochytskyi, Ukraine’s deputy minister of foreign affairs. “At a global scale, we ask to close the sky over the nuclear power plants in Ukraine.”

It’s not just Russia’s nuclear weapons fraying relations with the West. Earlier this week, Secretary of State Antony Blinken accused Russia of using Ukraine’s largest nuclear power plant as a “nuclear shield” during the war. Russia took over the plant in the early weeks of the invasion.

“Russia is now using the plant as a military base to fire at Ukrainians, knowing that they can’t and won’t shoot back because they might accidentally strike a nuclear reactor or highly radioactive waste in storage,” Blinken said. “That brings the notion of having a human shield to an entirely different and horrific level.”

This week’s developments came as a month-long U.N. conference to review the Nuclear Nonproliferation Treaty began Monday. They also came as the United States is considering a move to declare Russia as a sponsor of terrorism.

Last week, the Senate passed a nonbinding resolution urging Blinken to apply the label to Russia. Russian officials have threatened to break off diplomatic relations with Washington if that happens.

“The logical result of such a step becomes a break in diplomatic relations,” Russian Foreign Ministry spokeswoman Maria Zakharova said Tuesday. “Washington risks finally crossing the point of no return – with all the ensuing consequences. This should be well understood in Washington.”

The Associated Press, Reuters, and USA Today contributed to this report.