Iran’s Supreme Leader Ayatollah Ali Khamenei has on Sunday issued a stark warning to the United States, saying any military action against Iran would ignite a regional war. Addressing the nation, Khamenei said Iran had no intention of starting a war or attacking any country, but would respond “decisively and forcefully” if provoked. The remarks come amid heightened rhetoric from Washington and renewed focus on Iran following unrest inside the country and warnings linked to the death sentence given to a protester.

"The Americans should know that if they start a war, this time it will be a regional war," Khamenei was quoted as saying by the semi-official Tasnim news agency.

Donald Trump earlier said Iran was in "serious discussions" and he hoped they would lead to something "acceptable", while Iran's Foreign Minister Abbas Araghchi told CNN he was "confident that we can achieve a deal" on Tehran's nuclear programme.

Trump has threatened to intervene in Iran over its nuclear ambitions and after its deadly crackdown on anti-government protests.

Araghchi said, "Unfortunately, we have lost our trust [in] the US as a negotiating partner," but added the exchange of messages through friendly countries in the region was facilitating "fruitful" talks with Washington.

Iran's top security official Ali Larijani had previously said a framework for negotiations was progressing.

As part of its buildup of forces, the US has sent its aircraft carrier the USS Abraham Lincoln to the region and late last week US Central Command said it was operating in the Arabian Sea.