The US is ready to sit down for talks with Iran without conditions but sanctions and pressure will not be removed to pave the way for discussion, Secretary of State Mike Pompeo said on Sunday.
Iran’s destabilising regional interference would have to be discussed, Mr Pompeo said.
Until now, Iranian officials have dismissed the idea of talks without first removing sanctions reimposed when the US pulled out of the 2015 nuclear deal with world powers last year.
Over the past 13 months, America has increased pressure on Iran by banning oil exports and cutting off revenue for the government.
But on Saturday, Iran's President Hassan Rouhani suggested he may be willing to hold talks if Washington showed some respect.
But Mr Rouhani said Tehran would not be pressured into discussions.
"We are prepared to engage in conversations with no pre-conditions," Mr Pompeo said after the Iranian leader's comments.
"We’re ready to sit down with them but the American effort to fundamentally reverse the malign activity of this revolutionary force is going to continue.”
Switzerland has long represented the US interests in Iran, where America has no diplomatic mission, and has offered to again play intermediary between Tehran and Washington.
Mr Pompeo’s meeting with Swiss Foreign Minister Ignazio Cassis, in the southern town of Bellinzona, came amid concerns about the risk of escalation and miscalculation with Iran – a situation that has many in Europe and the Middle East on edge.
He said US President Donald Trump had been saying for a long time that he was willing to talk to Iran.
"We are certainly prepared to have that conversation when the Iranians can prove that they want to behave like a normal nation," Mr Pompeo said.
Mr Trump last Monday said he hoped Iran would come to the negotiating table and that he was confident he could make a deal.
But supreme leader Ayatollah Ali Khamenei said on Wednesday that Tehran would not negotiate with Washington, even after Mr Rouhani had signalled that talks might be possible if sanctions were lifted.
Last year, Mr Pompeo outlined 12 ways in which Iran must change, including stopping its support for proxy groups and halting its missile programme, before the US lifted sanctions.
He called on Iran to stop uranium enrichment, never to pursue plutonium reprocessing and to close its heavy water reactor.
Mr Pompeo said it also had to declare all previous military dimensions of its nuclear programme and to permanently and verifiably abandon such work.
Mr Cassis made no secret of his nervousness about the current situation.
“The situation is very tense," he said. "We are fully aware, both parties are fully aware, of this tension. Switzerland, of course, wishes there is no escalation to violence.
“Both parties are now increasing the pressure and for the rest, this is a matter of worry but we cannot do anything unless we get a mandate from both parties.”
Mr Cassis said Switzerland would be pleased to serve as an intermediary, but not a “mediator”, between the US and Iran.
Neither he nor Mr Pompeo would say if such requests had been made of the Swiss.
Mr Pompeo thanked Switzerland, which serves as the “protecting power” for the US in Iran, for looking after Americans detained there.
Trump administration officials have suggested they would look positively at any move to release at least five American citizens and at least two permanent US residents imprisoned in Iran.
Mr Pompeo said that the release of unjustly jailed Americans in Iran and elsewhere was a US priority.
Japanese Prime Minister Shinzo Abe is reportedly set to meet Iranian supreme leader Mr Khamenei this month. The news, still not confirmed officially, comes just days after US President Donald Trump visited Japan.
The report by Mainichi Shimbun, one of the largest papers in Japan, it would be the first such talks between a Japanese premier and Tehran's supreme leader.
Japan and Iran have maintained good relations for years as resource-poor Tokyo needs strong supplies of oil and gas to power the country, which is the fourth largest global consumer of oil.
This is despite Tehran supplying only 5.3 per cent of Japan’s energy supplies last year.
In 2004, Japan became a major investor in the Iranian energy business planning to develop the giant Azadegan oilfield.
But in the face of US concern, they scaled down involvement from a 75 per cent stake to 10 per cent in 2006, then fully divested in 2010.
Japanese-Iranian relations date back centuries but it has played a key role in recent years.
After the Iran-Iraq war ended in 1988, thousands took advantage of visa-free travel between the two countries and either moved for work or traded between Japan and Iran.
At least 50,000 Iranians were believed to be living in Japan in 1990 but that began to fall after 1992 when Tokyo ended the visa-free travel because of the worsening economic situation.
Some analysts believe Iran is acting to restore influence it has lost since Mr Trump withdrew from the 2015 nuclear deal and the US reimposed sanctions that have harmed Iran’s economy.
Last month, the administration ended sanctions waivers that had allowed certain countries to continue to import Iranian oil, the country’s main source of revenue, without US penalties.
The US also designated Iran’s Revolutionary Guards a “foreign terrorist organisation", adding new layers of sanctions to foreigners that did business with it or its affiliates.
Despite the US withdrawal, Iran has remained a party to the nuclear deal that involves the five permanent members of the UN Security Council, Germany and the EU.
Iran has continued to broadly comply with the terms, which called for it to curb its nuclear work in exchange for sanctions relief.
But on Friday, the UN nuclear watchdog reported that Iran might be in breach of limits on the number of advanced centrifuges it can use.
Tehran has also warned of plans to withdraw from some elements of the deal.
Mr Pompeo declined to comment on the findings of the International Atomic Energy Agency, other than to say the US was monitoring events in Iran.
“The world should be mindful of how we are watching closely how Iran is complying with the requirements that were set out,” he said.
