One example: Data on making uranium metal should have been disclosed, critics say.
The document is 15 pages long, and among other things, it describes procedures for fabricating hemispheres of uranium metal – key components for a nuclear weapon.
International inspectors since 2005 have known Iran had this paper in its possession, but they got a copy of it only last November. Tehran's explanation for its existence? Iranian officials say they received it unbidden in a pile of instructions that came with uranium-enrichment devices from Pakistan.
US officials – plus many experts outside government – don't buy this story. The paper, they say, is just one of a number of publicly known items related to Iran's nuclear program that have yet to be explained and appear suspicious.
"There are still outstanding issues, and some of them are pretty serious," says Sharon Squassoni, a senior associate in the nonproliferation program at the Carnegie Endowment for International Peace in Washington.
According to a recent US National Intelligence Estimate, Iran halted a clandestine nuclear-weapons program four years ago but continues to develop uranium-enrichment technology applicable to weapon development.
Iran has long insisted that its nuclear efforts are peaceful and intended to produce only electric power. According to Iranian officials, the latest report of the United Nations' nuclear watchdog, the International Atomic Energy Agency (IAEA), shows they have resolved all outstanding questions about their program.