With differences still unresolved and the deadline for a deal nearing, Iran and the U.S. have a choice to make: Extend nuclear talks for a second time or face the risk of renewed confrontation and armed conflict.

U.S. Secretary of State John Kerry meets Wednesday in Vienna with Iranian Foreign Minister Mohammad Javad Zarif to try and advance the talks and meet the target date of Nov. 24. But with less than six weeks left until Nov. 24, there may be no alternative to prolonging them.

Iran denies wanting nuclear weapons. But if the talks fail, Tehran will return to expanding programs that could be turned from peaceful purposes to making such arms. That in turn could revive the chance of a new Middle East conflict through attacks by Israel and possibly the U.S.

The Americans insist the focus remains on sealing a deal by the end of the current four-month extension, but refuse to rule out that they will continue past Nov. 24. Iranian Deputy Foreign Minister Abbas Araghchi said last week that Tehran is already talking to the U.S. and five other world powers at the talks about a possible extension.

That may not happen, though, if the critics have their way.

Opposition is certain from skeptics in U.S. Congress and from Iran’s hardliners. Both already fear a nuclear sellout. Seeing prolongation as a trick by the opponent to gain further advantage, they are likely to use all possible means to oppose it.

“I think the extension will be very difficult to negotiate,” said Gary Samore, who left the U.S. team negotiating with Iran last year. “It is likely to be strongly resisted both in Washington and Tehran.”

Samore, who is now with Harvard University’s Belfer Center for Science and International Affairs, said an extension is achievable only if both sides feel they have come away with rewards. The U.S. and its five negotiating partners must give Tehran added sanctions relief while talks continue, while Iran has to further reduce its nuclear activities.

For the U.S. administration, any extension may need to include persuading opponents in the U.S. Senate that it’s in Washington’s interests. The prospect that Republicans could win a majority in the Senate in Nov. 4 elections makes that a daunting proposition. That would mean if new sanctions legislation passes in the new year by a two-thirds majority, President Barack Obama would be powerless to veto it.

In Iran, restive hard-liners will likely embark on a big push against any extension effort. President Hassan Rouhani’s negotiating team has so far been supported by Supreme Leader Ayatollah Ali Khamenei. But a lack of agreement by Nov. 24 may sway Khamenei, who has frequently expressed distrust of U.S. aims at the talks even while backing the process up to now.

Senate skeptics are worried that any deal will relieve sanctions pressure on Iran without making a sizable dent in its ability to make a nuclear weapon. Iran’s powerful Revolutionary Guards and others voice the inverse concern — that their country will reverse decades of nuclear achievement and scrap its programs for insufficient economic advantage.

(AP)