Dr. ElBaradei has long been reluctant to adopt a confrontational strategy with Iran, an approach he considers counterproductive. Responding to calls for the report’s release, he has raised doubts about its completeness and reliability.

Last month, the agency issued an unusual statement cautioning it “has no concrete proof” that Iran ever sought to make nuclear arms, much less to perfect a warhead. On Saturday in India, Dr. ElBaradei was quoted as saying that “a major question” about the authenticity of the evidence kept his agency from “making any judgment at all” on whether Iran had ever sought to design a nuclear warhead.

Even so, the emerging sense in the intelligence world that Iran has solved the major nuclear design problems poses a new diplomatic challenge for President Obama and his allies as they confront Iran.

American officials say that in the direct negotiations with Iran that began last week, it will be vital to get the country to open all of its suspected sites to international inspectors. That is a long list, topped by the underground nuclear enrichment center under construction near Qum, that was revealed 10 days ago.

Iran has acknowledged that the underground facility is intended as a nuclear enrichment center, but says the fuel it makes will be used solely to produce nuclear power and medical isotopes. It was kept heavily protected, Iranian officials said, to ward off potential attacks.

Iran said last week that it would allow inspectors to visit the site this month. In the past three years, amid mounting evidence of a possible military dimension to its nuclear program, Iran has denied the agency wide access to installations, documents and personnel.

In recent weeks, there have been leaks about the internal report, perhaps intended to press Dr. ElBaradei into releasing it.