Iran needs to "confess" to running a secret nuclear weapons program up to 2003 or its claims of cooperating with a UN investigation of its past clandestine activities will be a sham, a senior US envoy said Friday. But Gregory L. Schulte, chief delegate to the International Atomic Energy Agency, said even such an admission would not result in the lifting of UN sanctions - or end the threat of new ones. For that, he told reporters, Iran needs to comply with UN Security Council demands to suspend uranium enrichment. Even if Iran makes full disclosures of its nuclear past, it "must still suspend enrichment related activities," Schulte said, adding that refusal to do so "violates Security Council resolutions and casts doubt on its leaders' ultimate intent." "Iran is already a danger in the Middle East," he said. "That danger only increases as Iran's leaders shorten the timeline to produce nuclear weapons." As the UN's nuclear watchdog, the IAEA has been probing Iran's nuclear programs since revelations four years ago that Teheran had conducted nearly two decades of secret atomic activities, including developing enrichment and working on experiments that could be linked to a weapons program. A recently published US intelligence assessment names the same year - 2003 - as the time Teheran stopped direct work on creating nuclear arms. Under a plan agreed to earlier this year between Iran and the Vienna-based IAEA, Teheran committed itself to answering all nagging questions about its past nuclear activities. That, by implication, included programs that could have weapons applications. But the plan makes no direct mention of a clandestine Iranian weapons program, and Teheran denies it ever tried to develop one. Thus, the demand by Washington was unlikely to be met. "We are looking for an acknowledgment that they had nuclear weapons," Schulte said. "The end of the year is rapidly approaching (and) we are waiting to see if Iran's leaders are ready to confess." IAEA chief Mohamed ElBaradei has said he wants to wrap up the probe by December. But diplomats accredited to the agency, who demanded anonymity because their information was confidential, told The Associated Press this week that the agency had run into unspecified obstacles, and noted Iranian officials were now talking about March as the new deadline - something they said the United States and its allies would be unlikely to accept. Iranian President Mahmoud Ahmadinejad has called the US intelligence estimate a "victory" for his country and officials of other governments have suggested it could relieve pressure on the Islamic republic. Schulte warned against such interpretations. Iran was engaged in a "concerted, covert program, conducted by military entities, under the direction of Iran's government," he said. "Iran's leaders could choose to restart that program."