A senior U.S. envoy dismissed increased Iranian willingness to answer questions about its nuclear program as a smoke screen on Wednesday and said it would not prevent the U.N. Security Council from imposing additional sanctions on Tehran.

"Iran is clearly trying to take the attention from its continued development of bomb-making capabilities, and I don't think the Security Council will be distracted," said Gregory L. Schulte, the chief U.S. delegate to the International Atomic Energy Agency. "We are continuing to move forward with other members of the Security Council on a third resolution."

Schulte was responding to news that Iran and the Vienna-based IAEA — the U.N. nuclear watchdog — had reached an agreement on a timetable to respond to lingering questions over Tehran's controversial nuclear activities.

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U.S. officials have previously told The Associated Press that Washington views recent signs of increased openness by Tehran as a "charm offensive" meant only to divide Security Council members and prevent them from agreeing on new sanctions, and Schulte's comments reinforced that view.

"If Iran's leaders truly want the world's trust, they would ... start to cooperate fully and unconditionally and suspend activities of international concerns," said Schulte, alluding to council demands that Tehran freeze its uranium enrichment program and stop construction of a plutonium-producing reactor.

Schulte spoke to selected reporters in a hastily arranged conference call a day after Iranian and IAEA officials announced they had worked out a schedule. The quick U.S response reflected American concern about possible erosion of support for new sanction through the Islamic republic's decision to stop stonewalling IAEA experts on some aspects of its nuclear program.

Full Iranian cooperation with the agency's nuclear probe is only one of the council's demands, and Schulte said Tehran must also meet all others to avoid new U.N. punishment.

Of most concern to the international community are activities that could lead to the making of nuclear weapons — enrichment, which can produce both fuel and the core of warheads, and the building of the reactor that when finished will produce plutonium — also weapons material.

"These activities are not necessary for peaceful purposes but are necessary to build a bomb, Schulte said.

Iranian and IAEA officials announcing their agreement in Tehran on Tuesday did not elaborate or provide more details, including whether Tehran was ready to answer all outstanding questions. But Schulte suggested otherwise.

"We understand there are real limitations with the plan," he said, including Iran's refusal to allow IAEA inspectors broad powers to conduct inspections of suspicious sites on short notice.

A diplomat accredited to the IAEA said there were other "omissions" in the time table. The diplomat, who demanded anonymity for discussing confidential information, declined to elaborate.

Iran has refused to answer questions about secret plutonium experiments in the mid-1990s and IAEA findings that Iran has not accounted for all the plutonium it has said it possessed. IAEA experts also want to know more about unexplained traces of plutonium and enriched uranium found last year at a nuclear waste facility, and about the so-called "Green Salt Project."

Diplomats told the AP last year that the agency was trying to follow up on U.S. intelligence that described the project as linking uranium enrichment-related experiments to nuclear-related high explosives and warhead design. Iran dismissed that intelligence as "based on false and fabricated documents."

Other IAEA findings of concern include traces of enriched uranium found at a military site, and Iranian diagrams the IAEA has seen that explain how to form uranium metal into the shape of a warhead.

Iranian officials have refused to answer questions about those findings for years, leaving the IAEA unable to determine the nature of Iran's nuclear program. Iran's refusal to cooperate prompted U.N. Security Council to become involved last year. The Security Council has imposed two sets of sanctions on Iran over the nuclear standoff.

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