BEIRUT (Reuters) - Iranian President Hassan Rouhani defended the nuclear deal with Western powers Saturday and said that U.S. President Donald Trump could not undermine it. Under the 2015 deal, Iran agreed to limit its disputed nuclear program in return for the easing of economic sanctions. However, Trump is expected to announce soon that he will decertify the deal, a senior administration official has said, in a step that potentially could cause the accord to unravel. “In the nuclear negotiations and agreement we reached issues and benefits that are not reversible. No one can turn that back, not Mr. Trump or anyone else,” Rouhani said at a ceremony at Tehran University marking the start of the university academic year, according to state media.  “Even if 10 other Trumps are created in the world, these are not reversible.” Trump, who has called the pact an “embarrassment” and “the worst deal ever negotiated”, has been weighing whether the deal serves U.S. security interests as he faces the Oct. 15 deadline for certifying that Iran is complying with its terms.     The prospect of Washington reneging on the deal has worried some of the U.S. allies that helped negotiate it, especially as the world grapples with another nuclear crisis, North Korea’s nuclear and ballistic missile development. If Trump does not certify that Iran is in compliance, the U.S. Congress will have 60 days to decide whether to reimpose sanctions waived under the deal. U.N. inspectors have verified Iranian compliance with the terms. Rouhani said Saturday that if the United States violated the deal then it would hurt its own reputation in the international community. “If America carries out any violations today, the whole world will condemn America. They will not condemn Iran,” Rouhani said, according to state media. “Then they will say why did you trust America and sign an agreement with them?” Separately, former Iranian president Mohammad Khatami has been forbidden from attending “public political, cultural and promotional ceremonies”, for a period of three months, two of his lawyers told the Iranian Labour News Agency (ILNA) on Saturday. Khatami has long been a lightning rod of criticism for hardliners who accuse him of fomenting unrest in the protests that followed the disputed election of president Mahmoud Ahmadinejad in 2009. Local media are forbidden from quoting Khatami in articles or publishing his image. The new restrictions were issued by Iranian security forces, Khatami’s lawyers told ILNA, and there does not appear to be any judicial mechanism to dispute the restrictions. In the lead-up to the presidential election last May, Khatami posted a message online encouraging his supporters to vote for Rouhani. Rouhani made a reference to the new restrictions placed on Khatami during his speech Saturday but did not name him. “If anybody repeats that people should come to the ballot box, they should be punished?” he said, according to ILNA. Khatami’s lawyers told ILNA that the restrictions began on the first day of the Iranian month of Mehr, which is Sept. 23.  