Iran's Hassan Rouhani cast doubt over the landmark 2015 nuclear agreement, threatening to walk away from the deal and restart the country nuclear program if the US continued to impose new sanctions against the Islamic Republic.

Rouhani warned that Iran could go nuclear again "in an hour and a day" if the US refused to cease its "threats and sanctions."

Read more: Four more years: Trump just latest challenge for Rouhani

"Those who try to return to the language of threats and sanctions are prisoners of their past delusions," Rouhani said in the televised parliamentary address. "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."

Each side has accused the other of violating the spirit the 2015 deal, which saw the world's leading power agree to lift sanctions against Iran in exchange for curbs on its nuclear program and caps on its uranium enrichment levels.

US President Donald Trump has repeatedly lambasted the nature of the deal, once describing it as the "worst deal ever."

Iran, meanwhile, has carried out a series of ballistic tests in recent weeks, prompting the US to respond by imposing sanctions against individuals and companies alleged to be supporting Iran's missile program. That, in turn, has only spurred the Iranian regime to ratchet up military spending by more than half a billion dollars (426 million euros) to fight Washington's "adventurism."

Rouhani admitted that he would prefer to stick to the nuclear agreement, but warned that this was not the "only option." 

The Iranian leader was re-elected in May, in what many viewed as a referendum on his more open, progressive policies and, ultimately, on the nuclear deal itself.

US 'no reliable partner'

Rouhani also singled out his US counterpart, Donald Trump, as an unreliable partner, not just for Iran, but also for other US allies.

Read more: Europe and USA on a collision course over Iran nuclear deal

The Iranian leader cited Trump's decision to withdraw from the Paris climate agreement and international trade deals, such as the Trans-Pacific Partnership.

"In recent months, the world has witnessed that the US, in addition to its constant and repetitive breaking of its promises in the JCPOA (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," Rouhani said.

dm/kms (AFP, AP)