That capped what had been an intense day of negotiations as the two sides seek what they have set up as a deal that would limit Iran`s nuclear activities in exchange for sanctions relief.
This round of talks, which builds on a framework agreement they reached in April, was due to end last week, but was extended by seven days. Now, officials from both sides have signaled more time may be needed.
"We don`t see definite deadlines," a senior Iranian official said Monday. "We know there are certain considerations by the U.S. That doesn`t mean everyone agrees."
If a deal is reached by Thursday, the U.S. Congress would have 30 days to review it and vote on whether to lift certain sanctions lawmakers have imposed. After Thursday, the review period becomes 60 days.
White House spokesman Josh Earnest said Monday that going beyond Tuesday`s deadline is "certainly possible."
Iran and the group of world powers have disagreed for months on items such as the pace at which sanctions would be lifted and the level of access that U.N. inspectors would have to Iranian sites in order to monitor compliance with an agreement.
But a new issue emerged Monday, with Iranian officials saying they want a U.N. arms embargo lifted, something Western officials said they oppose.
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