Iran signalled Sunday it favours a de-escalation after 10 days 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 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 in his occasional all-capitals style.
US Defence 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.
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In a meeting between Iran's President Hassan Rouhani and the visiting emir of Qatar, both sides agreed de-escalation is the "only solution" to the regional crisis, the emirate's ruler said.
Qatar hosts the largest US military base in the region but also enjoys strong ties with Iran, with which it shares the world's largest gas field.
"This visit comes at a critical time in the region," Emir Sheikh Tamim bin Hamad Al-Thani said on what was believed to be his first official visit to the Islamic republic.
"We agreed... that the only solution to these crises is de-escalation from everyone and dialogue."
For his part, Rouhani said: "Given the importance of security of the region... we've decided to have more consultations and cooperation for the security of the entire region."