A comprehensive nuclear agreement between six world powers and Iran will not be agreed upon until everything in it is agreed upon, US Under Secretary of State for Political Affairs Wendy Sherman said Saturday.

"There is only one measure of success of a comprehensive agreement with Iran, and that is if an agreement means that Iran will never obtain a nuclear weapon," Sherman told reporters in Jerusalem.

The top US negotiator in the negotiations over Iran's disputed nuclear program said final-deal talks, which began Tuesday in Vienna, were aiming to come to an agreement in July.

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