TEHERAN - Iran's Supreme Leader Ali Khamenei warned on Monday that any "wicked" action by the United States or Israel against Teheran would be met with a forceful retaliation.

Speaking at Imam Khomeini's Grand Mosalla mosque after leading Eid al-Fitr prayers, Khamenei said threats from Washington and Tel Aviv would not go unanswered.

"They threaten to carry out wicked acts against Iran," he said in remarks broadcast on his official website. "While we do not consider it very likely that such an act will be committed from outside the country, if it happens, they will definitely receive a reciprocal, hard blow."

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His comments came after former US President Donald Trump told NBC News on Sunday that the United States would launch unprecedented military strikes on Iran if it refused to negotiate over its nuclear program.

"If they don't make a deal, there will be bombing," Trump said. "It will be bombing the likes of which they have never seen before."

Trump said negotiations between Washington and Teheran were ongoing but did not provide details.

READ MORE: Iran's president rejects direct negotiations with Washington

On Sunday, Iranian President Masoud Pezeshkian confirmed that Teheran had formally rejected a recent US proposal for direct talks, conveyed in a letter from Trump. Addressing a cabinet meeting, Pezeshkian reiterated Iran's refusal to engage in face-to-face negotiations with Washington while sanctions remain in place but left open the possibility of indirect diplomacy.