Iran has rejected an informal meeting with U.S. and other powers to discuss the stalled 2015 nuclear agreement - insisting that the U.S. must first remove all sanctions, the Jerusalem Post said Monday.

An Iran foreign ministry official said it wasn't the proper time for the talks proposed by the European Union. The U.S. said it was disappointed but remained open to "reengage in meaningful diplomacy."

"Considering the recent actions and statements by the U.S. 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," CNBC quoted Iranian Foreign Ministry representative Saeed Khatibzadeh as saying.

With Iran accelerating its nuclear program in violation of the 2015 international nuclear accord and the U.S. launching airstrikes on Iran-backed militias in Syria, officials have warned opportunities to alleviate tensions might now be jeopardized.

Some nations suspect Iran has secret ambitions to advance its nuclear capabilities, a claim the country denies.

Then-President Donald Trump reimplemented economic sanctions to force Iran to renegotiate the 2015 deal. Iran refused and retaliated by abandoning a number of commitments.

A White House official said the U.S. would now discuss the issue with Britain, France, Russia, China and Germany.