Secretary of State John Kerry indicated on Sunday that Iran and six world powers were closing in on a nuclear deal, but said negotiators still had "a few tough things to do."
Negotiators have until Monday afternoon to secure a deal, after the deadline was extended on Friday. In a sign that something might be in the works, both Russian Foreign Minister Sergei Lavrov and Chinese Foreign Minister Wang Yi were expected to join the talks.
"I think we're getting to some real decisions," Kerry told reporters in the Austrian capital on Sunday morning. "So I will say, because we have a few tough things to do, I remain hopeful. Hopeful."
Iran and six powers — Britain, China, France, Germany, Russia and the United States — are attempting to end a more than 12-year dispute over Iran's atomic program by negotiating limits on its nuclear activities in exchange for sanctions relief.
The sides remain divided over issues that include a U.N. arms embargo on Iran that Western powers want to keep in place, access for inspectors to military sites in Iran and answers from Tehran over past activity suspected of military aims.
This story originally appeared on NBCNews.com