US Secretary of State Mike Pompeo also said that Washington would continue to exert pressure on Iran to change its behaviour. In response, Tehran has rebuked Pompeo's comments.
US Secretary of State Mike Pompeo said on Sunday that the Trump administration is ready for unconditional discussions with Iran in an effort to ease rising tensions that have sparked fears of conflict.
But the United States will not relent in trying to pressure the Islamic Republic to change its behaviour in the Middle East, America's top diplomat said.
Pompeo repeated long-standing US accusations that Iran is bent on destabilising the region, but he also held out the possibility of talks as President Donald Trump has suggested.
While the offer may not pan out, Pompeo made it during a visit to Switzerland, the country that long has represented American interests in Iran, as part of a European trip aimed at assuring wary leaders that the US is not eager for war.
"We're prepared to engage in a conversation with no preconditions," Pompeo told reporters at a news conference with his Swiss counterpart.
"We're ready to sit down with them, but the American effort to fundamentally reverse the malign activity of this Islamic Republic, this revolutionary force, is going to continue."
In response to Pompeo's offer, Tehran on Sunday ruled out talks with Washington unless it changes its "general behaviour".
"The change of the general behaviour and actions of the United States of America regarding the Iranian nation is the criterion" required for any talks to take place, said foreign ministry spokesman Abbas Mousavi.
"The Islamic Republic of Iran ignores word games and the use of new language to express secret aims," said Mousavi.
"Mr. Pompeo’s emphasis on maintaining maximum pressure on Iran reflects the continuation of the same faulty behaviour that must be corrected," the spokesman said, quoted in a ministry statement.
Europe, Mideast on edge
Pompeo's meeting with Foreign Minister Ignazio Cassis in the southern Swiss town of Bellinzona came amid concerns about the potential for escalation and miscalculation with Iran — a situation that has many in Europe and the Middle East on edge.
Cassis, whose country has been an intermediary between the two before, made no secret of that nervousness.
"The situation is very tense. We are fully aware, both parties are fully aware, of this tension. Switzerland, of course, wishes there is no escalation, no escalation to violence," he said.
"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."
Cassis said Switzerland would be pleased to serve as an intermediary, but not a "mediator," between the United States and Iran. To do so, however, would require requests from both sides, he said.
Neither he nor Pompeo would say if such requests had been made of the Swiss.
Pompeo thanked Switzerland, which serves as the "protecting power" for the United States 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 currently imprisoned in Iran.
Pompeo declined to comment on whether he had made a specific request to the Swiss about the detainees. But, he said the release of unjustly jailed Americans in Iran and elsewhere is a US priority.
Pompeo was in Switzerland on the second leg after Germany of a four-nation tour of Europe in which he is both trying to calm nerves and stressing that the US will defend itself and not relent in raising pressure on Iran with economic sanctions.
Despite the firm stance, Trump has signalled a willingness to talk with Iran's leadership. Iranian officials have hinted at the possibility but also insisted they will not be bulled.
"If they want to talk, I'm available," Trump said last week, even as Pompeo and the White House national security adviser, John Bolton, were stepping up warnings that any attack on American interests by Iran or its proxies would draw a rapid and significant US response.
The US is sending hundreds of additional troops to the region after blaming Iran and Iranian proxies for recent sabotage to tankers in the Persian Gulf and drone attacks on Saudi Arabia's oil infrastructure.
Some analysts believe Iran is acting to restore leverage it has lost since Trump withdrew from the 2015 nuclear deal and the U.S. reimposed sanctions that have hobbled 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 might do 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 European Union.
Iran has continued to broadly comply with the terms, which called for it to curb its nuclear work in exchange for sanctions relief. On Friday, however, the United Nations' nuclear watchdog reported that Iran may be in violation of limits on the number of advanced centrifuges it can use.
Pompeo declined to comment on the findings of the International Atomic Energy Agency other than to say the US is "watching closely" what is going on 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.