Iran Getting Close to the Bomb
Although Iran was pushing for an end to sanctions, they are delaying the process to have enough Uranium to have the potential to make the bomb to get a better deal from the U.S.
Since Trumps one sided exit from the Obama deal with Iran , Israel has pushed the U.S to add more demands on Iran. They do not want to have the Iranian ballistic Missile threat over their head. This additional demand which is totally unacceptable by Iran, has created the problem with negotiations.