In an August 2001 intelligence paper, department analysts warned of suspicious activities in Iraq that "could be preliminary steps" toward reviving a centrifuge program.

The inspectors found no trace of a clandestine centrifuge program.

We knew that Iran was working on a centrifuge program.

For example, "Gaps remain in the agency's knowledge" about the scope of Iran's centrifuge program, the report said.

It remains possible that the electromagnetic separation program and the centrifuge program were also intended to operate in harness rather than independently.

He said that while investigators had identified the main components of the centrifuge program, they still could not be sure that the Iraqis were not concealing something.

And for now, at least, Iran's centrifuge program appears to have hit some technical hitches.

It also called on Iran to answer critical lingering questions about the scope of its centrifuge program and the source of the technology.

The provenance of the North Korean centrifuge program is a useful lesson in nuclear proliferation.

The North Koreans have reluctantly admitted that they have a centrifuge program but have not let any foreign observers see it.