The 2015 nuclear accord has been unravelling since last year when the United States unilaterally withdrew from it and began reimposing sanctions on Iran.

The three European countries still party to the deal -- Britain, France and Germany -- have been trying to salvage it but their efforts have so far borne little fruit.

"If they use the trigger (mechanism), Iran would be forced to seriously reconsider some of its commitments to" the International Atomic Energy Agency, said parliament speaker Ali Larijani.

"If they think doing so is more beneficial to them, they can go ahead," he told a news conference in Tehran.

In May, one year after the US pullout, Iran began retaliating by scaling back its commitments to the deal -- known formally as the Joint Comprehensive Plan of Action.

Following its latest step back this month, the European parties warned the JCPOA's dispute resolution mechanism could be triggered if Iran continued down that path.

It covers various stages that could take several months to unfold, but the issue could eventually end up before the UN Security Council, which could decide to reimpose sanctions.

Larijani also suggested the current deadlock with the United States could be "fixed" if Iran's arch-foe learns from the past.

Ahead of the 2015 deal, then US president Barack "Obama wrote a letter and said that I accept Iran's enrichment, now let's negotiate," he said.

"If the American officials have just as much wisdom, to use past experiences, then they can fix this issue."

The JCPOA set out restrictions on Iran's nuclear programme in exchange for the lifting of Western sanctions.