TEHRAN: A defiant Iran vowed on Saturday to press ahead with its missile programme and condemned new US sanctions, as tensions rise after the West hardened its tone against the Islamic republic, reports AFP.

In the latest incident on the ground, Iran's Revolutionary Guards said the US Navy had approached their patrol vessels in the Gulf and fired flares.

"At 4 pm (1130 GMT) on Friday, the supercarrier USS Nimitz and its accompanying warship, while being monitored by the Guards' frigates, flew a helicopter near the Resalat oil and gas platform and approached the force's ships," the paramilitary force said.

"The Americans in a provocative and unprofessional move, sent a warning message to the frigates and fired flares," it said. The Guards "ignored the unconventional move by the US ships and continued their mission."

Three days earlier, a US Navy patrol ship fired warning shots at a Guards boat in the Gulf as it closed in on the American vessel, according to US officials.

The Guards denied approaching the US ship in Tuesday's incident and said it was the American vessel that had been at fault.

There have been a string of close encounters between US ships and Iranian vessels in the Gulf in recent months.

On the political battlefield, Iranian foreign ministry spokesman Bahram Ghasemi told state broadcaster IRIB that Tehran condemned new US sanctions against its missile programme, which President Donald Trump is set to sign into law, and vowed to press on.

"We will continue with full power our missile programme," he said. "We consider the action by the US as hostile, reprehensible and unacceptable, and it's ultimately an effort to weaken the nuclear deal."

Ghasemi was referring to a 2015 agreement between Iran and US-led world powers that lifted some sanctions on Tehran in return for curbs on the country's nuclear programme.