Supreme Leader Ali Khamenei said Iran had nothing to be concerned about, in his first reaction since the return of biting US sanctions on Tuesday. "With regard to our situation do not be worried at all. Nobody can do anything," his website Khamenei.ir quoted him as saying, according to Reuters. US President Donald Trump tweeted on Tuesday that the new sanctions, which were lifted under a 2015 international nuclear deal, were the most biting sanctions ever imposed. Companies doing business with Iran will be barred from the United States, Trump said. Iranian Foreign Minister Mohammad Javad Zarif told the Iran newspaper that Oman and Switzerland have acted as mediators in talks with America in the past but that there are currently no direct or indirect talks being held with the United States. He also denied that he met with US Secretary of State Mike Pompeo in Singapore last week. Iranian President Hassan Rouhani, speaking in a meeting with North Koreas foreign minister on Wednesday, said that America cannot be trusted, according to the State news agency IRNA. "Today, America is identified as an unreliable and untrustworthy country in the world which does not adhere to any of its obligations," Rouhani said. In the current situation, friendly countries should develop their relations and cooperation in (the) international community," he said, adding Iran and North Korea have "always had close views" on many issues. Ri traveled to Tehran after attending a security forum in Singapore, where he and Pompeo sparred over an agreement made at Junes landmark summit between Trump and North Korean leader Kim Jong Un.