Fischer told private German news channel N-TV he had "great concern" over news Tehran broke seals placed on enrichment equipment by the International Atomic Energy Agency and threatened to resume the manufacture and assembly of centrifuges.
Under a deal brokered in October with Britain, France and Germany, Iran agreed to suspend sensitive uranium enrichment programs, stop making centrifuges, allow tougher inspections and file a complete declaration of its nuclear activities.
But an intelligence report circulated by diplomats this week alleges Iranian officials were caught negotiating with a Russian company over the procurement of a substance that can boost nuclear explosions in atomic weapons.
Iran denies it is developing nuclear arms and claims its nuclear program is solely intended for peaceful purposes.
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