US President Donald Trump has announced the immediate start of new nuclear weapons tests, citing testing programmes in other countries.

"Because of other countries testing programs, I have instructed the Department of War to start testing our Nuclear Weapons on an equal basis," Trump wrote in a post on his Truth Social platform on Thursday.

"That process will begin immediately," he added, without specifying which weapons would be tested.

The announcement came shortly before Trump's meeting with Chinese President Xi Jinping in South Korea. During the talks, Trump declined to answer a reporter's question about the planned nuclear tests.

The United States and China are established nuclear powers, along with Russia, Britain and France.

According to a report by the Stockholm International Peace Research Institute (SIPRI), there are currently nine nuclear-armed states, including India, Pakistan, North Korea and Israel.

Nuclear tests would be the first in over 30 years

If the US were to carry out nuclear weapons tests for the first time in more than 30 years, other nuclear powers could also be prompted to act. The United States last conducted a nuclear test in 1992, at what is now known as the Nevada National Security Site.

The US retains the capability to resume testing at the location, and under certain conditions, the president can authorize such tests, according to the Congressional Research Service.

Following Trump's announcement, opposition emerged in Congress. "Absolutely not. I'll be introducing legislation to put a stop to this," Democratic Representative Dina Titus of Nevada wrote on X.

Just days earlier, Russian President Vladimir Putin emphasized the military strength of nuclear power during a meeting with his general staff at a command centre in an undisclosed location.

Putin said the Russian military has achieved numerous successes in the war against Ukraine and confirmed that the recent test of the long-range nuclear missile Burevestnik had been a success.

In his Truth Social post, Trump claimed that the United States possesses more nuclear weapons than any other country.

However, according to the International Campaign to Abolish Nuclear Weapons (ICAN), Russia currently holds the largest confirmed stockpile with more than 5,500 warheads, while the US has around 5,044.