With a deadline just hours away, negotiators from the United States, Iran and five other nations appeared on Tuesday to move closer to a preliminary political accord to limit Tehran’s nuclear program . There were signs, however, that several of the most difficult issues would be deferred for a final agreement in three months. In Moscow, Sergey V. Lavrov, Russia’s foreign minister, said that there was a strong chance of an accord and that he was flying to back to Switzerland on Tuesday, after leaving the day before, to rejoin the talks. “The chances are high,” Mr. Lavrov said. “They are probably not 100 percent, but you can never be 100 percent certain of anything. The odds are […]