Kerry would "gauge Iran's willingness to make the critical choices it needs to make," a senior State Department official said.
"The Secretary will take the time necessary to have that discussion, and that's why they will be meeting again today, to see if progress can be made," the official added.
British Foreign Secretary William Hague said on Sunday it was crucial for Iran "to be more realistic about what is necessary" to reach a nuclear deal with six major powers that would end sanctions against Tehran in exchange for curbs on its atomic work, adding that no breakthroughs had been achieved and there was "no major change in the state of play in these negotiations as of this moment".
Hague was speaking to reporters after a meeting with Kerry. Together with their French and German counterparts, they are in Vienna to help break a deadlock in the nuclear negotiations with Iran, a week before a deadline to reach an agreement.
Austrian Foreign Minister Sebastian Kurz said that Austria was willing to host the nuclear talks with Iran even if they were not finished on Sunday and would have to be prolonged. Furthermore he said that he hoped that the negotiations would "not be terminated".
Iran denies seeking the atomic bomb and wants the lifting of all UN and Western sanctions, which have crippled its economy.