VIENNA (AP) - Diplomats say Iran is moving ahead to update a programme the West fears could be used to make nuclear weapons, in a blow to years of high-level diplomacy aimed at stopping it from doing so.

Three diplomats say Teheran now has installed about 700 high-tech centrifuges in an upgrade of its uranium enrichment programme since the start of the year. That represents an increase of about 100 since mid-April.

Teheran says it is enriching uranium only for peaceful uses. But the US and its allies fear that Teheran may enrich to levels used for nuclear bombs.

The International Atomic Energy Agency (IAEA) is expected to report on the development on Wednesday. The diplomats, all from IAEA member nations, demanded anonymity because they are not authorised to divulge confidential IAEA information.