Dubai - New US sanctions against Iran's supreme leader and foreign minister have closed off diplomacy, Iran said on Tuesday, blaming the United States for abandoning the only route to peace just days after the two foes came within minutes of conflict.
US President Donald Trump signed an executive order imposing sanctions on Monday against Supreme Leader Ali Khamenei and other senior figures. Sanctions against Foreign Minister Mohammad Javad Zarif are expected later this week.
The moves came after Iran shot down a US drone last week and Trump called off a retaliatory air strike minutes before impact, which would have been the first time the United States had bombed Iran in decades of hostility between them.
Trump said he decided at the last minute that too many people would die.
"Imposing useless sanctions on Iran's Supreme Leader and the commander of Iran's diplomacy is the permanent closure of the path of diplomacy," Iranian Foreign Ministry spokesman Abbas Mousavi said on Twitter.
"Trump's desperate administration is destroying the established international mechanisms for maintaining world peace and security," Mousavi tweeted.
In a televised address, President Hassan Rouhani said sanctions against Khamenei would have no practical impact because the cleric had no assets abroad.
Rouhani, a pragmatist who won two elections on promises to open Iran up to the world, described the U.S. moves as desperate and called the White House "mentally retarded", an insult Iranian officials have used in the past about Trump but a departure from Rouhani's own comparatively measured tone.
Rouhani and his cabinet run Iran's day-to-day affairs, while Khamenei, in power since 1989, is Iran's ultimate authority.
"The White House actions mean it is mentally retarded," Rouhani said. "Tehran's strategic patience does not mean we have fear."
Trump's hawkish national security adviser, John Bolton, visiting Israel, repeated earlier offers to hold talks, as long as Iran was willing to go beyond the terms of a 2015 nuclear deal with world powers which Trump abandoned last year.
"The president has held the door open to real negotiations to completely and verifiably eliminate Iran's nuclear weapons programme, its pursuit of ballistic missile delivery systems, its support for international terrorism and other malign behaviour worldwide," Bolton said in Jerusalem. "All that Iran needs to do is to walk through that open door."
The United States has imposed crippling economic sanctions against Iran since last year, when Trump withdrew from an agreement between Tehran and world powers to curb Iran's nuclear programme in return for the lifting of sanctions.
The crisis has escalated sharply since last month, when the Trump administration tightened the sanctions, ordering all countries to halt purchases of Iranian oil.
That effectively starved the Iranian economy of the main source of revenue Tehran uses to import food for its 81 million people, and left Iran's pragmatic faction with no benefits to show for its nuclear agreement.
Washington says the 2015 agreement reached under Trump's predecessor Barack Obama did not go far enough because it is not permanent and does not cover issues beyond the nuclear programme, such as missiles and regional behaviour.
Iran says there is no point negotiating with Washington when it has abandoned a deal that was already reached.
The downing of the US drone - which Iran says was over its air space and the United States says was international skies - was the culmination of weeks of rising tensions that had begun to take on a military dimension.
The United States and some regional allies have blamed Iran for attacks on tankers in the Gulf, which Tehran denies. Washington's European allies have repeatedly warned both sides of the danger that a small mistake could lead to war.
Washington says forcing Iran to the table is the purpose of its sanctions. Tehran has said it is willing to talk if the United States lifts the new sanctions first, although Tuesday's statements appear to toughen that stance.
US officials have launched a diplomatic campaign to rally their allies in the face of the escalating crisis. Foreign Secretary Mike Pompeo jetted to the Middle East on Monday to meet leaders of Saudi Arabia and the United Arab Emirates, Gulf Arab states that favour the toughest possible line against Iran.
The US envoy on Iran, Brian Hook, is visiting Europe, where he is likely to get a frostier reception from allies who support the nuclear deal. They believe Trump's decision to quit the accord was a mistake that has strengthened Iran's hardline faction, weakened its pragmatists and endangered regional peace.
Iran says it still aims to comply with the nuclear deal, but cannot do so indefinitely unless it receives some benefits. It has given European countries until July 8 to find a way to shield its economy from U.S. sanctions, or else it will enrich uranium to levels banned under the deal.