US President Donald Trump has issued a stern warning to Iran, suggesting it will be destroyed if a conflict breaks out between the two countries.
"If Iran wants to fight, that will be the official end of Iran," he said in a tweet on Sunday. "Never threaten the United States again!"
The US has deployed additional warships and planes to the Gulf in recent days.
But Mr Trump's tweet marks a shift in tone after recent attempts to downplay the possibility of military conflict.
Only a matter of days ago, the president told aides that he did not want US pressure on Iran to turn into a conflict.
And when asked by reporters last Thursday if the US was going to war, Mr Trump answered: "I hope not."
Iran has also moved to talk down concerns over the escalating tensions. On Saturday, its foreign minister insisted there was no appetite for war.
"There will not be a war since neither we want a war nor does anyone have the illusion they can confront Iran in the region," Mohammad Javad Zarif told state news agency Irna.
The latest frictions come after Iran suspended its commitments under the 2015 international nuclear deal, and threatened to resume production of enriched uranium which is used to make reactor fuel and nuclear weapons.
The deal aimed to cut sanctions on Iran in exchange for an end to its nuclear programme, but the US unilaterally withdrew from the agreement last year.
BDST: 1114 HRS, MAY 20, 2019