The United Nations chief Antonio Guterres on Thursday warned of the risks associated with nuclear testing.

"Current nuclear risks are already alarmingly high, and all actions that could lead to miscalculation or escalation with catastrophic consequences must be avoided," Farhan Haq, a spokesperson for Guterres said.

The statement comes as President Donald Trump appeared to suggest the U.S. will resume testing nuclear weapons for the first time in three decades, saying it would be on an “equal basis” with Russia and China.

The Kremlin pointed out that a global ban on nuclear tests has remained in place, but warned that if any country resumes nuclear testing Russia would follow suit.

There was no indication the U.S. would start detonating warheads, but Trump offered few details about what seemed to be a significant shift in U.S. policy.

He made the announcement on social media minutes before he met with Chinese leader Xi Jinping on Thursday in South Korea to discuss trade. He offered little clarity when he spoke to reporters later aboard Air Force One as he flew back to Washington.

The U.S. military already regularly tests its missiles that are capable of delivering a nuclear warhead, but it has not detonated the weapons since 1992. The Comprehensive Nuclear Test Ban Treaty, which the U.S. signed but did not ratify, has been observed since its adoption by all countries possessing nuclear weapons, North Korea being the only exception.

Trump suggested, however, that changes were necessary because other countries were testing weapons. It was unclear what he was referring to, but it evoked Cold War-era escalations.