US President Donald Trump on Saturday pledged to hit Iran with "major" new sanctions as Tehran warned Washington that any attack would see its interests across the Middle East go up in flames.
The war of words heated up after Trump had pulled back from military action against Iran in response to its downing of a US reconnaissance drone.
Trump, who spent Saturday huddling with his advisors at Camp David, initially told reporters that he was keen to be Iran's "best friend" -- if the country agreed to renounce nuclear weapons.
"When they agree to that, they're going to have a wealthy country. They're going to be so happy, and I'm going to be their best friend," he told reporters.
Iran has denied seeking a nuclear weapon and says its program is for civilian purposes.
A multinational accord reached by Tehran and world powers in 2015 sought to curb Iran's nuclear ambitions in exchange for sanctions relief.
But Trump left that agreement more than a year ago and has imposed a robust slate of punitive economic sanctions designed to choke off Iranian oil sales and cripple its economy -- one he now plans to expand.
"We are putting major additional Sanctions on Iran on Monday," tweeted Trump, who has also deployed additional troops to the Middle East.
"I look forward to the day that Sanctions come off Iran, and they become a productive and prosperous nation again - The sooner the better!"
Added Secretary of State Mike Pompeo: "When the Iranian regime decides to forgo violence and meet our diplomacy with diplomacy, it knows how to reach us. Until then, our diplomatic isolation and economic pressure campaign against the regime will intensify."
But lest anyone think he was entirely ruling out military action, Trump tweeted Saturday evening that "I never called the strike against Iran 'BACK,' as people are incorrectly reporting, I just stopped it from going forward at this time!"
'Powder keg'
A top Iranian military official warned Washington against any strikes.
"Firing one bullet towards Iran will set fire to the interests of America and its allies" in the region, armed forces general staff spokesman Brigadier General Abolfazl Shekarchi told the Tasnim news agency.
"If the enemy -- especially America and its allies in the region -- make the military mistake of shooting the powder keg on which America's interests lie, the region will be set on fire," Shekarchi warned.
Agence France-Presse