Iran on Monday signalled it favours a de-escalation after more than a week of heightened tensions with the United States during which both sides fired missiles and Tehran accidentally shot down a passenger aircraft.
Security was stepped up in Iran's capital Sunday after a vigil the previous night for those killed in the air disaster turned into an angry protest and police temporarily arrested the British ambassador for being there.
US President Donald Trump warned Iran against harming demonstrators and against a repeat of a deadly crackdown against rallies in November sparked by a fuel price hike.
"To the leaders of Iran — DO NOT KILL YOUR PROTESTERS," Trump tweeted Sunday in his occasional all-capitals style.
US Defense Secretary Mark Esper, however, said Trump was still willing to "sit down and discuss without precondition a new way forward" with Iran, although Tehran has steadfastly refused to hold talks with Washington unless it lifts sanctions first.
Tehran said it favoured an easing of tensions after its arch-enemy Washington on January 3 killed a revered Iranian general, Quds Force chief Qasem Soleimani, in a Baghdad drone strike.