Secretary of State John F. Kerry arrived in Vienna on Thursday for what he hopes will be the culmination of laborious negotiations aimed at curbing Iran’s ability to build a nuclear weapon and easing debilitating sanctions on the country’s economy.

On a stop in Paris en route to Vienna, Kerry said negotiators are focused on finalizing a deal by the time an interim agreement dies at midnight Monday — although it is expected that the talks could continue until dawn Tuesday.

“We are not talking about an extension,” Kerry said. “We are talking about getting an agreement.”

In contrast, other officials already are predicting that talks are likely to continue for weeks or months. Kerry’s remarks appear designed to pressure Iran to offer more concessions, including allowing U.N. monitors to make on-demand inspections at Iranian nuclear facilities.

Kerry has been on a whirlwind tour conferring with officials in the six-nation group that is negotiating with Iran: the five permanent U.N. Security Council members plus Germany. In Vienna, he conferred with American negotiators, then met separately with Iran’s foreign minister, Mohammad Javad Zarif, and Catherine Ashton, the European Union’s representative at the talks.

U.S. Secretary of State John Kerry , right, and Iranian Foreign Minister Javad Zarif, left, greet each other, as EU envoy Catherine Ashton watches, before a meeting in Vienna November 20, 2014. (Leonhard Foeger/Reuters)

Many analysts believe that the fate of the talks will ultimately be sealed in Washington and Tehran, where enmity and distrust run deep and where the political will to finalize a deal is most in doubt.

Iran seeks relief from economic sanctions in exchange for greater international monitoring and a scaling back of its nuclear program. But it insists it will not fully give up its ability to enrich uranium, the process to create nuclear fuel that can power reactors for energy and medical uses.

The United States and its allies fear that Iran could someday boost uranium enrichment levels to make material for a nuclear weapon. They are seeking reductions in the number of centrifuges Iran is using for enrichment and cuts in its uranium stockpiles. They want levels low enough that it would take Iran at least a year to enrich enough uranium for a bomb.

The United Nations’ nuclear watchdog, the International Atomic Energy Agency, also wants greater access to certain sites, including a military base near Tehran, to investigate claims of possible tests related to nuclear arms technology and to prevent any covert attempts to build a bomb.

“We are united . . . in our sense of where the issues are, what the issues are and what we need to do,” Kerry said after meeting with his French counterpart, Laurent Fabius, whose nation has sometimes been at odds with Washington over the direction of the talks.

Kerry said the United States is not willing to make a deal with Iran just for the sake of making a deal.

“We hope that those gaps that exist — and they do exist — can be closed. . . . We hope we can define the finish line.”

The gaps are why British and Russian officials have warned that an extension of the deadline may be needed to work out the details. But delays could embolden hard-liners in Iran who are opposed to a deal involving the United States, and a new Republican-led U.S. Congress seeking increased sanctions against Tehran.

Working in favor of a deal is the concern that the alternative — a collapse of the talks — could be worse.

“To walk away is not an option,” said Kelsey Davenport, director for nonproliferation policy at the Arms Control Association. “That way, nobody wins. It would be likely to lead to an escalation — more sanctions on the U.S. side, possibly Iran ramping up its nuclear capacity.”

Reza Marashi, research director for the Washington-based National Iranian American Council, said the Iranian government is under pressure from its citizens to find a way to escape sanctions that have caused rising prices and led to cuts in subsidies and to a scarcity of goods, including medical supplies.

Apart from the technical issues, he said, Iran wants a face-saving deal it can sell as a victory.

“Most important on the Iranian side is the idea of dignity and respect,” he said. “Iran wants to be treated as a partner,” not to be patronized.

Murphy reported from Washington.