(CNN) The Biden administration is disappointed after Iran rejected an offer by the European Union to partake in nuclear talks with the US and the other signatories of the nuclear deal on Sunday, but said they remain open to diplomacy with Iran.
"While we are disappointed at Iran's response, we remain ready to reengage in meaningful diplomacy to achieve a mutual return to compliance with JCPOA (Joint Comprehensive Plan of Action) commitments," a White House spokesperson said.
"We will be consulting with our P5+1 partners on the best way forward," the spokesperson added. The P5+1 refers to the permanent members of the UN Security Council -- China, France, Russia, the United Kingdom and the United States -- and Germany.
The Wall Street Journal first reported on Iran's rejection.
Iran's rejection of the Biden administration's first effort to jumpstart diplomacy and begin drawing both Iran and the US back into compliance with the nuclear deal signals how long and complicated the diplomatic process aimed at salvaging the deal is expected to be.
Iran's Foreign Ministry spokesman Saeed Khatibzadeh said Sunday that now is not a good time for the meeting.
The rejection comes just days after the US military struck a site in Syria used by Iranian-backed militia groups in response to recent rocket attacks on American forces in the region in the past two weeks.
"Up to a handful" of militants were killed in the strikes, a US official previously told CNN. The site was not specifically tied to the rocket attacks, but Secretary of Defense Lloyd Austin said he was "confident" it was used by the same Iranian-backed Shia militias targeting US and coalition forces in Iraq with rocket attacks.
"This is not very encouraging," said a European diplomat familiar with Iran's rejection. Iran wants a guarantee of sanctions relief after the meeting, the diplomat said.
The Biden administration, which views this move by Iran as part of the diplomatic process, has maintained that they are flexible about the format of these talks. But the longer it takes to get Iran to the table for talks, the more challenging it will be to salvage the situation, the European diplomat said.
The International Atomic Energy Agency and Iran reached a "technical understanding" last weekend in an effort to prevent a complete breakdown of the deal that will be in place for up to three months. The agreement had to be put into place because Iran moved forward with one of its most egregious violations of the JCPOA to date: curbing short-notice inspectors.