"They are continuing with contracts with local firms to assemble centrifuges. That is something we don't view favorably," a Western diplomat close to the Vienna-based International Atomic Energy Agency (IAEA) told AFP.

Iran had pledged in November to suspend uranium enrichment as a confidence-building measure to show the IAEA it was not secretly trying to develop nuclear weapons.

And in December Tehran ended the months of wrangling by signing a key UN treaty protocol allowing surprise inspections of its nuclear facilities.

But Iran has interpreted the pledge over suspending uranium enrichment in a narrow sense, stopping such activities at its Natanz nuclear fuel-making plant, but continuing to assemble centrifuges in case it decides to resume making highly-enriched uranium, which can be used both as fuel for reactors or to make a bomb, diplomats said.

"We know that the IAEA and Iran continue to negotiate on the terms of the suspension. Some things are agreed. Others aren't," a diplomat said.

The US spokesman for Washington's IAEA mission in Vienna, Michael Garuckis, said: "The scope of the suspension must be comprehensive."

Another diplomat said he was sure the Iranians were not at this time importing equipment for nuclear technology.

IAEA spokesman Mark Gwozdecky refused comment beyond saying that "at Iran's and the (IAEA) board of governors request we are monitoring Iran's suspension of enrichment-related activities and will report on this to the next scheduled meeting of the board (in March)."

The Islamic republic has been accused by the United States of secretly trying to develop atomic weapons, charges it has vigorously denied.

WAR.WIRE