Mike Pompeo's warning came a day after the head of the IAEA urged Iran to respond to its concerns.

US Secretary of State Mike Pompeo on Tuesday accused Iran of "possible undeclared nuclear activities," as the UN's nuclear watchdog presses Tehran for answers on its atomic safeguards.

"The Iranian regime's lack of full cooperation with @iaeaorg raises questions about possible undeclared nuclear material or activities," Mike Pompeo tweeted.

"The world won't fall for it. We will deny the regime all paths to a nuclear weapon."

Mike Pompeo's warning came a day after the head of the International Atomic Energy Agency (IAEA) urged Iran to respond quickly to its concerns, as the troubled 2015 deal with world powers over Tehran's nuclear program threatens to fall apart.