Four "western" Foreign Ministers flew to Vienna today to further negotiate about Iran's nuclear achievements. It is quite dubious why Kerry thought that such a meeting now would be helpful. It looks like this was planned as an attempt to intimidate Iran into further concessions but failed because neither Russia's nor China's Foreign Minister are attending.
The negotiations are supposed to find a compromise until July 20. After that the negotiations would have to be prolonged for another 6 month which would only give more time to those who are against any deal to sabotage it.
The two sticking points are "breakout capacity" and the length of the period Iran would restrict itself to a certain limits of its industrial nuclear capacities. The "breakout capability" is a quite weird concept described as the total centrifuge capacity and thereby capability to produce enough enriched Uranium for one sole bomb in a certain time frame. Of course no state wanting a nuclear deterrent would use its officially declared, and highly controlled capacities to produce the materials needed. Nor would the reach of a "one bomb" capability be significant in any strategic sense.
But the U.S. negotiators seem to stick to the concept of arbitrarily limiting enrichment capabilities while even very seasoned U.S. proliferation experts find that it not helpful and that it risks to make any deal impossible:
So the most realistic goal in Vienna isn’t to make breakout impossible, but to make it a difficult and unattractive option for Iran. Once you see that as the goal, you realize that the gains in transparency from any likely deal—extremely close monitoring of declared facilities and the power to inspect undeclared facilities—should be at the forefront of American thinking about this problem. It would be a mistake to sacrifice such transparency in a failed attempt to reduce Iran’s breakout capacity by some arbitrary increment that is actually less valuable than many in Washington think it is.
The Chinese and Russian seem see the U.S. concept of "breakout capability" as a sham that is used to sabotage the talks:
Vladimir Evseyev of the Russian state-run CIS institute says Washington’s insistence that Iran shut down uranium enrichment facilities and negotiate on its missile program violates the accords outlining the scope of the talks. The U.S., he said, wants negotiations to “to be lengthy and painful,” so as to keep sanctions in place for its own political agenda.
Diplomats familiar with the talks say Moscow shares Washington’s desire to reach a deal but is significantly less demanding of Tehran. While the U.S. wants deep cuts in Iranian programs that could be used to make nuclear arms, Russia would settle for pervasive monitoring, they say.
The Chinese and Russians are agreeing with the U.S. proliferation experts. The "breakout capability" is nonsense and good monitoring is much more important than any numerical capacity restriction.
That "western" states use the concept of "breakout capacity" at all can only be interpreted as their unwillingness of reaching a deal with Iran.