DUBAI - Six world powers will help Iran redesign its Arak heavy water reactor so that it cannot produce weapons-grade plutonium, according to a document released by the state news agency IRNA on Saturday.

The document was signed separately on Nov. 13, 17 and 18 by the foreign ministers of Iran and the P5+1 (the United States, Britain, France, China and Russia plus Germany) as well as EU foreign policy chief Federica Mogherini. It became effective on the date it was signed by all states.

The fate of the Arak reactor in central Iran was one of the toughest sticking points in the long nuclear negotiations that led to an agreement in July. Removing the core of the heavy water reactor to produce less plutonium is a crucial step before the relief from sanctions starts.

Iran will act as project manager, according to the document, while China "will participate in the redesign and the construction of the modernized reactor" and the United States "will provide technical support and review of the modernized reactor design". France, the United Kingdom and Germany will participate in design review and Russia will provide consultative services.(Reuters)