Iranian MPs attend a session of the National Assembly in Tehran. (Photo: AFP/VNA)

The letter, signed by 250 of 290 members parliament says the other parties should guarantee that they will not exit a restored agreement, nor trigger the "snapback mechanism" under which sanctions on Iran would be immediately reinstated if it fails compliance.

The letter also says a return to the deal will only go ahead if all sanctions are lifted, including those pertaining to terrorism, missile technology, and human rights.

In addition, lawmakers first want to confirm that Iran receives money from its exports, before the government returns to nuclear compliance.

The statement comes in the midst of final efforts in Vienna to revive the 2015 nuclear deal, which could lead to an agreement "very soon", according to a senior European Union official.