UNITED NATIONS - US President Donald Trump said on Wednesday that he had made his decision on whether or not the United States will remain in a 2015 nuclear accord between Iran and world powers, but he declined to reveal it."I have decided," Trump told reporters when asked if he had made up his mind after having criticized the accord under which Iran agreed to curb its nuclear program in return for relief from economic sanctions.Responding to Trump's comments, a senior Iranian official told Reuters Iran was prepared for all scenarios if the United States walked out on the agreement and was capable of resuming its restricted nuclear activities immediately if necessary. US officials have sent mixed signals about the nuclear agreement hammered out between Iran and six major powers - Britain, China, France, Germany, Russia and the United States.In a pugnacious speech on Tuesday before the UN General Assembly annual gathering of world leaders, Trump called the accord "an embarrassment." On Wednesday, US Ambassador to the United Nations Nikki Haley said Trump's speech indicated his unhappiness but not a decision to abandon the accord."It's not a clear signal that he plans to withdraw. What it is, is a clear signal that he's not happy with the deal," Haley, told CBS News in an interview.Trump hinted in his speech to the annual gathering of world leaders that he may not recertify the agreement, negotiated by his predecessor, Barack Obama. "I don't think you've heard the last of it," he said. The US president must decide by Oct. 15 whether to certify that Iran is complying with the pact, a decision that could sink the deal. If he does not, the US Congress has 60 days to decide whether to reimpose sanctions waived under the accord.Under the agreement between Iran and six major powers - Britain, China, France, Germany, Russia and the United States - the Iranian government agreed to restrict its nuclear program in return for western countries loosening economic sanctions.Haley spoke ahead of Iranian President Hassan Rouhani's UN speech in which he is expected to respond to Trump's accusations that Iran exports "violence, bloodshed and chaos." The head of Iran’s Revolutionary Guards said the United States should experience "painful responses" following Trump's harsh criticism."Taking a definitive stand against Trump is only the beginning of the path," said General Mohammad Ali Jafari, according to Sepah News, the news site of the Revolutionary Guards. "What is strategically important is that America witnesses more painful responses in the actions, behavior and decisions that Iran takes in the coming months." The prospect of Washington reneging on the agreement has worried some US partners that helped negotiate it, especially as the world grapples with another nuclear crisis, North Korea’s nuclear and ballistic missile development.Russia is concerned by Trump questioning the Iran nuclear deal, Foreign Minister Sergei Lavrov told Russian reporters at the United Nations in comments published by his ministry on Wednesday."It's extremely worrying," Lavrov said. "We will defend this document, this consensus, which was met with relief by the entire international community and genuinely strengthened both regional and international security." Lavrov, referring to Trump's speech, said that "if you simply condemn and threaten, then we're going to antagonize countries over whom we want to exert influence."