VIENNA - A landmark nuclear accord sealed last year between Iran and six world powers will not be in danger if Donald Trumps wins the US presidential election in November, the head of Iran's Atomic Energy Organisation said on Wednesday.Republican presidential candidate Trump has called the accord "the worst deal ever negotiated" and said it could even lead to "nuclear holocaust", although he has also conceded it would be hard to rip up a deal enshrined in a UN resolution.Trump has also blasted his Democrat rival Hillary Clinton for her role as Secretary of State in 2009-13 in helping to pave the way for the talks culminating in the deal, which curbs Tehran's nuclear activities in exchange for sanctions relief.However, Iran's Ali Akbar Salehi played down the possibility that Trump might turn his back on the accord."I think whoever gets into the ... office of the president in the United States will have to move according to the realities on the ground," he told a panel discussion in Vienna."You can (use) many words, slogans, but then at the end of the day you are constrained by the realities."Salehi said the accord included necessary mechanisms for dealing with the contingency of one side breaching it. "I don't think (the nuclear deal would receive) any serious impact (from Trump). It may go a little bit up and down, it may delay certain things, but it will not seriously detract (from the deal)."