Updates with additional details
US president Donald Trump said he called off talks with Tehran in the latest attempt to pressure the Iranian government beset by nationwide protests.
"I have cancelled all meetings with Iranian Officials until the senseless killing of protesters STOPS," Trump posted on his social media platform on Tuesday, urging the demonstrations to carry on.
Trump said on 11 January that Iran's leaders had reached out to him to negotiate, without providing details. Iran has not explicitly confirmed having reached out to Trump for the resumption of talks.
Trump returned to the topic of Iran throughout Tuesday, without providing a clear statement on what he plans to do.
The White House previewed a scheduled speech Trump planned to give in Detroit, Michigan, as possibly outlining his plans for Iran. But Trump merely restated his earlier social media post and claimed that his threat to impose a 25pc tariff on US imports from countries doing business with Iran went into effect Tuesday.
The White House has not made public any executive order on new tariffs, and the Customs and Border Patrol agency's tariff portal makes no mention of them either.
China is Iran's largest trading partner and the primary destination for Iranian crude, which reaches independent refiners through a well-established network of traders and tankers designed to avoid US sanctions.
In later remarks to reporters, Trump again mulled possible US air strikes in Iran but declined to explain how that would help protect protesters in Iran. "You never know," he said. "So far, my track record has been excellent."
Trump also downplayed possible retaliation by Tehran. "Iran said that the last time I blew them up with the nuclear capability, which they don't have any longer," he said.
Iran's leaders "have got a big problem, and I hope they're not going to be killing people," Trump said. "It would seem to me that they have been badly misbehaving," he said, but added, "That is not confirmed."
Public demonstrations began in several Iranian cities on 28 December in protest at deteriorating economic conditions, and unrest has escalated in scope and severity, particularly over the past week or so, which has triggered a crackdown by state security forces.
The US oil industry has offered a cautious reaction to the prospect of the US getting involved in Iran, in the wake of another military operation against Venezuela.
"We're monitoring that situation," industry group American Petroleum Institute president Mike Sommers said Tuesday at his group's annual event. "We don't know what the next steps are," Sommers said.
"This is good news for the Iranian people, though," he said. "They're taking freedom into their own hands. Our industry is committed to being a stabilizing force in Iran if they decide to overturn the regime."
The US is not importing Iranian crude but "the challenge in these conflicts is really what happens to the US consumer," refiner Marathon Petroleum chief executive Maryann Mannen said.
"As we know, just when we think about the control over the strait [of Hormuz] or how long any disruption might be …. we certainly can survive for a period of time," Mannen said.
