Iran's nuclear chief said Wednesday his "gut feeling" was that Donald Trump would not rip up last year's landmark atomic accord between major powers and the Islamic Republic if the US Republican presidential hopeful was elected.

"Whoever becomes US president will have to adapt to the reality on the ground," Ali Akbar Salehi was quoted by the Austria Press Agency as saying in a speech in Vienna.

"Things could go up and down a bit, and some things could get delayed but nothing will be seriously in danger," APA, in German, quoted Salehi as saying.

He said his "gut feeling" was that no one really wanted to go back on the July 2015 pact that ended a long-running standoff that had poisoned Iran's external relations.

Under the agreement, Iran dramatically scaled back its nuclear activities in order to put atomic weapons out of Tehran's reach, an aim Tehran always denied having.

In return, the UN and Western countries lifted painful sanctions that had throttled Iran's all-important oil exports.

Trump, running against Hillary Clinton to be elected US president on November 8, said on March 21 that his "number one priority" in foreign policy would be to dismantle the "disastrous" deal.