The head of the United Nations nuclear oversight agency said Monday that his organization was in a 'stalemate' with Iran over its suspected nuclear program, just after the Iranian president affirmed once again that his country would not stop uranium enrichment or negotiate over its nuclear rights. Mohamed ElBaradei, the head of the International Atomic Energy Agency, told the group's 35-nation board that Iran had not stopped enriching uranium or answered lingering questions about its nuclear program. He urged Iran to 'substantively re-engage' with the nuclear agency, and to 'respond positively to the recent U.S. initiative' on a dialogue about nuclear issues. President Barack Obama and his European allies have given Iran until the end of September to respond to an offer of nuclear talks with the 'five plus one' group of permanent U.N.Security Council members and Germany. If Iran refuses, it could face harsher sanctions. In a news conference in Tehran on Monday, the Iranian president, Mahmoud Ahmadinejad, said he was ready to hold 'fair and logical' talks to 'solve global challenges' with the six-nation group. 'We will continue our work in the framework of global regulations and in close cooperation with the International Atomic Energy Agency,' said Ahmadinejad, who won a second term after a disputed election in June that set off widespread protests and the worst internal unrest Iran has seen in decades. But Ahmadinejad also made clear that Iran expects a 'change of approach' from the other side, and it was not even clear whether nuclear issues would be on the agenda. He said, as he has in the past, that 'the nuclear issue is over' from Iran's point of view. Iran has repeatedly denied accusations that it is developing nuclear weapons, and has refused to stop enriching uranium, citing its right to enrich uranium under the nonproliferation treaty. 