Diplomats are scrambling to reach consensus just hours ahead of a self-imposed deadline on the outline of an Iran nuclear deal.

Facing a midnight local time (6 p.m. EDT) Tuesday target to produce a framework agreement, substantial differences persisted. Top diplomats from the five permanent members of the U.N. Security Council and Germany were meeting alone and then with Iran's foreign ministers to try to bridge the remaining gaps. They hope to hammer out an understanding that would serve as the basis for a final accord to be reached by the end of June.

The latest round of negotiations began last Thursday in the Swiss town of Lausanne. Officials have cited some progress in the talks, which have as yet failed to nail down an agreement.