President Donald Trump said he could negotiate with Tehran “if and when they are ever ready”, less than 24 hours after he threatened that Iran would meet its end if it fought the US.
Mr Trump sent mixed signals about Iran on his Twitter account on Monday.
He denied reports that the US was trying to set up a negotiating channel with Iran but also appeared confident that Tehran would would want talks with the US.
"In the meantime, their economy continues to collapse," Mr Trump wrote. "Very sad for the Iranian people.”
He and his Secretary of State, Mike Pompeo, have been nudging Iran towards negotiations.
“I would like to see them call me,” Mr Trump said last week before tweeting late on Wednesday that Iran “will want to talk soon".
He then held a surprise meeting with Swiss President Ueli Maurer at the White House.
Switzerland has been the official protector of US interests in Iran since Washington and Tehran broke off relations in 1980. It has also helped to mediate between the two.
Mr Pompeo and the US special representative on Iran, Brian Hook, have been urging Tehran to meet and negotiate a new nuclear deal that addresses regional concerns.
“If they're prepared to come to the table and negotiate those things to get to that outcome, fantastic,” Mr Pompeo said last month.
He called Omani Sultan Qaboos on Thursday and discussed the situation in Yemen and Iranian threats to the Gulf region.
In 2011, Oman hosted US officials and enabled secret, unofficial talks between the Obama administration and Iran, which culminated in the nuclear deal in 2015.
Omani Foreign Minister Yusuf bin Alawi arrived in Tehran on Monday and met his Iranian equal Javad Zarif.
Despite this, recent events suggest the pressure is increasing between Washington and Tehran.
Iran has increased the enrichment of low-grade uranium fourfold, saying stockpile limits under the 2015 nuclear deal no longer applied, Tasnim news agency announced on Monday.
Saudi Arabia is calling for an Arab League summit to discuss the Iranian threat after an attack on its oil pipeline and two pumping stations.
Two US warships have arrived in the region and the US and states have increased naval patrols in the Gulf of Oman.
UN Secretary General Antonio Guterres called for calm, urging all parties involved to stand back.
Mr Guterres was also concerned at the rocket launch that seemed to be aimed at the US embassy in the Iraqi capital, Baghdad.
“It is a very volatile region," UN spokesman Stephane Dujarric said on Monday.
"Any developments, whether they are action on the ground or whether they are rhetoric, can always be misinterpreted and can only heighten the risk of a volatile region becoming even more volatile.”
