The US is not planning to conduct nuclear explosions, Energy Secretary Chris Wright has said, calming global concerns after President Donald Trump called on the military to resume weapons testing.

"These are not nuclear explosions," Wright told Fox News on Sunday. "These are what we call non-critical explosions."

The comments come days after Trump wrote on Truth Social that he had directed defence officials to "start testing our nuclear weapons on an equal basis" with rival powers.

But Wright, whose agency oversees testing, said people living in the Nevada desert should have "no worries" about seeing a mushroom cloud.

"Americans near historic test sites such as the Nevada National Security Site have no cause for concern," Wright said.

"So you're testing all the other parts of a nuclear weapon to make sure they deliver the appropriate geometry, and they set up the nuclear explosion."

Trump's comments on Truth Social last week were interpreted by many as a sign the US was preparing to restart full-scale nuclear blasts for the first time since 1992.

In an interview with 60 Minutes on CBS, which was recorded on Friday and aired on Sunday, Trump reiterated his position.

"I'm saying that we're going to test nuclear weapons like other countries do, yes," Trump said when asked by CBS's Norah O'Donnell if he planned for the US to detonate a nuclear weapon for the first time in more than 30 years.

"Russia's testing, and China's testing, but they don't talk about it," he added.

Russia and China have not carried out such tests since 1990 and 1996 respectively.

Pressed further on the topic, Trump said: "They don't go and tell you about it."

"I don't want to be the only country that doesn't test," he said, adding North Korea and Pakistan to the list of nations allegedly testing their arsenals.

On Monday, China's foreign ministry denied conducting nuclear weapons tests.

As a "responsible nuclear-weapons state, China has always... upheld a self-defence nuclear strategy and abided by its commitment to suspend nuclear testing", spokeswoman Mao Ning said at a regular press conference in Beijing.

She added that China hoped the US would "take concrete actions to safeguard the international nuclear disarmament and non-proliferation regime and maintain global strategic balance and stability".

On Thursday, Russia too denied it had carried out nuclear tests.

"Regarding the tests of Poseidon and Burevestnik, we hope that the information was conveyed correctly to President Trump," Kremlin spokesman Dmitry Peskov told journalists, referencing the names of Russian weapons. "This cannot in any way be interpreted as a nuclear test."

North Korea is the only country that has carried out nuclear testing since the 1990s - and even Pyongyang announced a moratorium in 2018.

The exact number of nuclear warheads held by each country is kept secret in each case - but Russia is thought to have a total of about 5,459 warheads while the US has about 5,177, according to the Federation of American Scientists (FAS).

The US-based ACA gives slightly higher estimates, saying America's nuclear stockpile sits at about 5,225 warheads, while Russia has approximately 5,580.

China is the world's third largest nuclear power with about 600 warheads, France has 290, the United Kingdom 225, India 180, Pakistan 170, Israel 90 and North Korea 50, the FAS says.

According to the US think tank Centre for Strategic and International Studies (CSIS), China has roughly doubled its nuclear arsenal in the past five years and is expected to exceed 1,000 weapons by 2030.