Iran’s President Hassan Rouhani has denounced possible new US sanctions on his country which, if enacted, could jeopardise a hard-won nuclear deal due to be finally implemented within weeks.

In a letter to his defence minister Rouhani said on Thursday reports that the US Treasury planned to blacklist companies and individuals with ties to Iran’s ballistic missile programme constituted "hostile and illegal interventions" that justified a response.

His comments came as relations worsened after US defence officials said an Iranian vessel had test-fired several rockets near three Western warships, including the USS Harry S Truman aircraft carrier, in the strategic Strait of Hormuz.

Iran’s powerful Revolutionary Guards, who are responsible for protecting Iranian interests in the Strait and regularly patrol and conduct exercises in the area where much of the world’s oil passes, denied its ships were involved.

Spokesman General Ramezan Sharif accused the US of fabricating the alleged December 26 incident as part of a "psychological operation".

"The Guards’ naval force had no exercise in the past week when the Americans claim that a missile or rocket was fired in the Hormuz Strait area," he said.

Though the rockets were not fired toward any warship, their proximity to them and several commercial vessels – reportedly around 1,500 yards (metres) – was "highly provocative", said a US official.

A French frigate and the USS Bulkeley destroyer were also in the area at the time.

Responding to the threat of new sanctions, Rouhani, under whom Iran negotiated the nuclear deal with the US and five other world powers, warned of reprisals.

Should individuals and companies be added to "the previously unjustified sanctions list, it is necessary that the production of various missiles required by the armed forces move forward with increased speed and seriousness," Rouhani wrote to Defence Minister Hossein Dehghan.

The president’s comments were also posted on his official Twitter account.

In the five months since the nuclear deal was struck, US officials say Iran has conducted two ballistic missile tests, one of which state media reported at the time, on October 11.

Iran also recently aired television footage of an underground missile base.

A United Nations panel found earlier this month that the missile tests breached previous UN resolutions aimed at stopping Iran from developing missiles capable of carrying a nuclear warhead.

Tehran has always denied seeking an atomic weapon.

The nuclear deal was heralded by moderates such as Rouhani, who staked his reputation on the negotiations, but hardliners in Tehran said it damaged Iran’s national interests. 

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