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The US says Iran can undertake some construction work at a key nuclear facility as long as fuel isn't produced and advances aren't made on a planned heavy water reactor.
The Arak site was among the thorniest issues negotiators sought to resolve in last weekend's nuclear agreement in Geneva.
The White House said afterword Iran wouldn't advance its "activities" at Arak or progress toward plutonium production. It spelled out several more constraints.
Iranian Foreign Minister Mohammad Javad Zarif said today while his country was honouring the deal, construction on building projects would continue.
State Department spokeswoman Jen Psaki says she isn't sure what work Zarif meant. She says road or building work might be allowable. But nuclear fuel production, reactor work, testing, control systems advances and other activities aren't permissible.
