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Hassan Rouhani issued a direct threat in a speech to parliament, claiming Iran can restart its nuclear programme"in an hour and a day" if Washington continues with "threats and sanctions".

He warned that Tehran was ready to walk out of the 2015 deal, which saw the lifting of most international sanctions in return for curbs on its nuclear program, if Washington persisted.

"Those who try to return to the language of threats and sanctions are prisoners of their past delusions," he said in his address, which was televised.

"If they want to go back to that experience, definitely in a short time - not weeks or months, but in the scale of hours and days - we will return to our previous situation very much more stronger."

Rouhani said his country ideally preferred to stick to the nuclear deal, which he called "a model of victory for peace and diplomacy over war and unilateralism".

But he also warned that the accord with the US, Russia, China and three EU countries was not the "only option" for Iran.

His comments come with the nuclear deal under mounting pressure after Tehran carried out missile tests and strikes, and Washington imposed new sanctions. Each sides has accused the other of violating the spirit of the agreement.

The Iranian president also hit out at US counterpart Donald Trump saying that he had shown the world that Washington was "not a good partner", not just for Iran but for US allies.

"In recent months, the world has witnessed that the US, in addition to its constant and repetitive breaking of its promises in the [nuclear deal] has ignored several other global agreements and shown its allies that the US is neither a good partner nor a reliable negotiating party," he said. 

Rouhani, a 68-year-old moderate cleric, won a resounding re-election victory in May in large part due to the backing of reformists who supported his message of greater civil liberties.