Iran has ruled out holding an informal meeting with the US and European powers on ways to revive a nuclear deal, insisting that America must lift all of its unilateral sanctions first.
Iran's foreign ministry spokesman said it was not an appropriate time for the talks proposed by the European Union.
The US said it was disappointed but that it remained ready to "re-engage in meaningful diplomacy" on the issue.
Tensions have soared since the US left a nuclear deal with Iran in 2018.
Then-President Donald Trump re-imposed crippling economic sanctions to force Iran to renegotiate the 2015 accord, known as the Joint Comprehensive Plan of Action (JCPOA). Iran refused and retaliated by rolling back a number of key commitments.
The US has now expressed intent to rejoin the deal under President Joe Biden. But Washington insists Tehran must return to full compliance with the agreement first, while Iran says that will only happen once sanctions are lifted.
Iran nuclear crisis: The basics
- World powers don't trust Iran: Some countries believe Iran wants nuclear power because it wants to build a nuclear bomb - it denies this.
- So a deal was struck: In 2015, Iran and six other countries reached a major agreement. Iran would stop some nuclear work in return for an end to harsh penalties, or sanctions, hurting its economy.
- What is the problem now? Iran re-started banned nuclear work after former US President Donald Trump pulled out of the deal and re-imposed sanctions on Iran. Even though new leader Joe Biden wants to rejoin, both sides say the other must make the first move.
"Considering the recent actions and statements by the United States and three European powers, Iran does not consider this the time to hold an informal meeting with these countries, which was proposed by the EU foreign policy chief," spokesman Saeed Khatibzadeh was quoted by Iranian media as saying.
A White House spokesman said the US would now consult with other parties to the nuclear deal - the UK, France, China, Russia and Germany - "on the best way forward".
Last Tuesday, Iran started to restrict some site inspections by the International Atomic Energy Agency (IAEA). The move is aimed at putting further pressure on the US and other parties to the JCPOA to get Washington to lift sanctions on its oil, banking and financial sectors.