US Secretary of State John Kerry is consulting with allies on how to overcome deep obstacles to reach a nuclear deal with Iran, three days before the deadline.
The State Department said Mr Kerry will meet German Foreign Minister Frank-Walter Steinmeier when he arrives in Vienna later today.
Mr Kerry also plans to talk to French Foreign Minister Laurent Fabius, who already is in the Austrian capital, as well as others by telephone.
The US and Iran remain divided on how much Tehran needs to constrain programmes that could make nuclear weapons.
Iran says all its programmes are meant for peaceful uses, but is negotiating because a deal would result in sanctions relief.
The differences are expected to result in the talks being extended beyond the Monday target date for a deal.