article_snippet: (CNN)Nuclear talks intensified Sunday between world powers and Iran, but key sticking points remained unresolved as the countries tried to reach a deal to curb Tehran's nuclear program ahead of a Tuesday deadline.
article_snippet: CNN)Nuclear talks had hit a snag on Saturday, with diplomats describing Iran as refusing to budge, but as the French, German and Chinese foreign ministers arrived, the mood seemed more optimistic.
article_snippet: U.S. officials and Western diplomats described the negotiations as tough and intense, which was expected as CNN)Nuclear talks reached the endgame.
article_snippet: On Saturday, Iranian Foreign Minister Mohammad Zarif made clear the issue of sanctions remains a stumbling block, saying Iranian Foreign Minister Mohammad Zarif believes the world powers "have realized that sanctions, pressure and an agreement will not go together.
article_snippet: It can also be characterized as the other side's intransigence in the talks.
article_snippet: Tuesday is seen as a critical milestone to the U.S. negotiators, who are trying to thwart a threat from Congress to impose additional sanctions without the  framework.