WASHINGTON, United States (AFP) — President Donald Trump landed back in the United States Thursday after a surprise directive to begin nuclear weapons testing that raised the specter of renewed superpower tensions.

The announcement on social media was issued right as Trump was going into a summit with Chinese leader Xi Jinping in South Korea.

And it came days after Russia declared it had tested a nuclear-capable cruise missile and a nuclear-powered, nuclear-capable sea drone.

The blunt statement from Trump, who boasts frequently about being a “peace” president, left much unanswered.

Chiefly, it was unclear whether he meant testing weapons systems or actually conducting test explosions — something the United States has not done since 1992.

Regardless, the statement amounted to unusual nuclear sabre rattling.

“Because of other countries testing programs, I have instructed the Department of War to start testing our Nuclear Weapons on an equal basis,” Trump said on Truth Social.

Trump also claimed that the United States has more nuclear weapons than any other country and that he had achieved this in his first term as president.

The Stockholm International Peace Research Institute (SIPRI) says in its latest annual report that Russia possesses 5,489 nuclear warheads, compared to 5,177 for the United States and 600 for China.

In his post, Trump said — minutes ahead of his Xi summit — said China was expected to “be even within 5 years.”

Chinese foreign ministry spokesman Guo Jiakun urged the United States to “earnestly abide” by a global nuclear testing ban.

The Kremlin questioned whether Trump was well-informed about Russia’s military activities.

The recent weapons drills “cannot in any way be interpreted as a nuclear test,” spokesman Dmitry Peskov told journalists. “We hope that the information was conveyed correctly to President Trump.”

Peskov then implied that Russia would conduct its own live warhead tests if Trump did it first.

“If someone departs from the moratorium, Russia will act accordingly,” Peskov said.

Both countries observe a de facto moratorium on testing nuclear warheads, though Russia and the US do regularly run military drills involving nuclear-capable systems.

The United States has been a signatory since 1996 to the Comprehensive Nuclear-Test-Ban Treaty, which bans all atomic test explosions, whether for military or civilian purposes.

Trump told reporters aboard Air Force One that it had been “many years” since the United States had conducted nuclear tests, but it was “appropriate” to start again.

Further muddying the waters, Trump also repeated in his remarks to reporters a previous claim that he wants negotiations on reducing nuclear weapons forces.

“Denuclearization would be a tremendous thing,” he said. “It’s something we are actually talking to Russia about, and China would be added to that if we do something.”

The United States conducted 1,054 nuclear tests between July 16, 1945, when the first test was conducted in New Mexico, and 1992, as well as two nuclear attacks on Japan during World War II.

It is the only country to have used nuclear weapons in combat.

The last US nuclear test explosion was in September 1992, with a 20-kiloton underground detonation at the Nevada Nuclear Security Site.

Then-president George H.W. Bush imposed a moratorium on further tests in October 1992 that has been continued by successive administrations.

Nuclear testing was replaced by non-nuclear and subcritical experiments using advanced computer simulations.

Nevada congresswoman Dina Titus responded that she would introduce legislation to “put a stop” to any move at restoring live weapons testing in her state.

And Senator Jacky Rosen, also a Democrat, said on X that Trump’s statement “directly contradicts the commitments I secured from Trump nominees… who’ve told me explosive nuclear testing would not happen & is unnecessary.”