WASHINGTON -- The United States used its negotiations with Iran to attempt to "infiltrate" the country with its influence, Supreme Leader Ayatollah Ali Khamenei said on Wednesday, forbidding future direct talks with the superpower.Khamenei, who delivered the remarks in Tehran to Revolutionary Guards commanders and repeated on his English-language Twitter feed, struck a discordant note with that of Iranian President Hassan Rouhani, who spoke to the United Nations last week. At the body's annual general debate, Rouhani suggested an international dialogue over the fractious war gripping Syria.Also at the UN the same day, before shaking hands with Iranian Foreign Minister Mohammad Javad Zarif at a luncheon, US President Barack Obama said that realism dictated he negotiate with any nation, "including Russia and Iran," to resolve the Syrian conflict, which has taken the lives of an estimated 300,000 people.The reason for the ban on negotiations, Khamenei said, is that Washington "took any chance to infiltrate" Iran during the nuclear talks, which concluded in July. The "Iranian side was vigilant, but they gained chances & acted against our national interests," he said."An important part of the activities of the enemy is to change the calculations of officials and to manipulate people’s revolutionary and religious thoughts," Khamenei continued. "Young people are the main target, and they must be alert."Khamenei also spoke of the strike on a hospital in Kunduz, Afghanistan, conducted by American forces. The attack, which the Pentagon has called a "mistake," killed 22 civilians."They consider no value for human lives; they attack a hospital, murder tens of patients and simply say ‘sorry, it was a mistake!'," Khamenei said.