"While we are disappointed at Iran's response, we remain ready to re-engage in meaningful diplomacy to achieve a mutual return to compliance with Joint Comprehensive Plan of Action (JCPOA) commitments," a White House spokesperson said on Sunday. 

"We will be consulting with our P5+1 partners on the best way forward," Xinhua news agency quoted the spokesperson as further saying. 

The White House's response came after Iran's Foreign Ministry spokesman Saeed Khatibzadeh said earlier on Sunday that the time was "not appropriate" for Tehran to hold an informal meeting with European countries and the US. 

"Considering the recent positions and actions of the US and three European countries, the Islamic Republic of Iran does not consider the time to be appropriate for an informal meeting proposed by the European coordinator of the JCPOA," he said. 

The road ahead is very clear, the spokesman said, adding that the US should end its "illegal" and unilateral sanctions and return to its JCPOA commitments. 

Last week, the European Union offered to attend an informal meeting between Iran and other parties to the JCPOA, which refers to the 2015 Iran nuclear deal, with the US also attending as a guest. 

In December 2020, the country's Parliament passed the law of "Iran's Strategic Action Plan to Counter Sanctions" which obliges the government to further reduce the obligations under the 2015 nuclear deal unless the US lifts sanctions against the Islamic Republic. 

As a result of the US' unilateral 2018 exit from the nuclear agreement, Iran has surpassed JCPOA-stipulated limits on its uranium enrichment level and on its stockpiles of heavy water and low-enriched uranium. 

The Islamic Republic has also lifted JCPOA limitations on its nuclear research and development activities.