As Iran and six world powers are preparing for a fresh round of nuclear talks in New York, a US negotiator says the two sides remain far apart on some key issues related to Iran’s nuclear energy program. US Under Secretary of State Wendy Sherman said on Tuesday that certain disputes over some leading dimensions of Iran’s uranium enrichment activities remain to be resolved. She added that Iran and the P5+1 have "identified potential answers to some key questions." However, she warned "we remain far apart on other core issues, including the size and scope of Iran's uranium enrichment capacity." Sherman said the world will only agree to suspend and lift the sanctions on Iran if Tehran takes convincing and verifiable steps to show that its nuclear program is and will remain entirely peaceful. "We must be confident that any effort by Tehran to break out of its obligations will be so visible and time-consuming that the attempt would have no chance of success," Sherman said. The ideas that the US and its allies have put forward to reach a final agreement by a November 24 deadline are "fair, flexible and consistent with Iran's civilian nuclear needs and scientific know-how," she added. The US negotiator’s remarks came as the International Atomic Energy Agency (IAEA) has repeatedly asserted that Iran is complying with efforts to reach a final deal to resolve the differences over its nuclear activities. As Iran and the P5+1 group are scheduled to hold the seventh round of nuclear talks in New York on Thursday, some experts have noted that excessive demands put forth by the US during the talks, including the demand for unlimited access to Iran's military sites, will finally lead the negotiations to failure. According to the latest reports, the United States, in its most recent negotiations with Tehran, called for extensive inspections of Iran’s military sites, which have nothing to do with the country’s nuclear energy program. Last November, Tehran and the five permanent members of the UN Security Council -- Russia, China, France, Britain, and the US – plus Germany signed an interim deal in Geneva, which took effect on January 20 and expired six months later. In July, Iran and the six countries agreed to extend negotiations until November 24 after they failed to reach common ground on a number of key issues.