Unless the P5+1 nations can specify exactly what Iran would need to do in order to begin to ease the sanctions, further talks – planned for next month in Moscow – seem like a waste of everyone's time.
The sanctions appear to be a one-way street: They are easy to enact as punishment, but evidently cannot be removed to reward positive Iranian behavior. The net result is that the Iranian people suffer, the Iranian regime keeps stockpiling more and more enriched uranium, and the US congressional hawks can feel smug in the false knowledge that continued sanctions will magically lead to regime change in Tehran.
In fact, a careful reading of the legislative text of the sanctions shows that the sanctions have very little to do with Iran's nuclear program and everything to do with regime change. For instance, the US sanctions can only be lifted after the president certifies to Congress:
that the government of Iran has: (1) released all political prisoners and detainees; (2) ceased its practices of violence and abuse of Iranian citizens engaging in peaceful political activity; (3) conducted a transparent investigation into the killings and abuse of peaceful political activists in Iran and prosecuted those responsible; and (4) made progress toward establishing an independent judiciary.
Just in case those conditions are insufficiently implausible, the president has to certify further that "the government of Iran has ceased supporting acts of international terrorism and no longer satisfies certain requirements for designation as a state sponsor of terrorism; and [that] Iran has ceased the pursuit, acquisition, and development of nuclear, biological, chemical, and ballistic weapons."