Trump shocks world with nuke test order

US President Donald Trump's surprise directive to begin nuclear weapons testing provoked global criticism on Friday, as it raised the specter of renewed superpower tensions.

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The announcement on social media was issued just before Trump -- who boasts frequently about being a peace president -- went into a summit with Chinese leader Xi Jinping in South Korea.

Trump's announcement left much unanswered -- chiefly whether he meant testing weapons systems or actually conducting test explosions, something the United States has not done since 1992.

Key US foe Iran on Friday called the directive "regressive and irresponsible", adding that it was a threat to international security.

"A nuclear-armed bully is resuming testing of atomic weapons. The same bully has been demonizing Iran's peaceful nuclear program," foreign minister Abbas Araghchi posted on social media.

Japanese atomic bomb survivors group Nihon Hidankyo sent a letter of protest to the US embassy in Japan on Friday.

The directive "directly contradicts the efforts by nations around the world striving for a peaceful world without nuclear weapons and is utterly unacceptable," the Nobel Peace Prizewinning group said in the letter obtained by AFP.

GLOBAL NUCLEAR TESTING BAN