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

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

Iran denies wanting nuclear weapons. But if the talks fail, Tehran will return to expanding programmes 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 the Israelis and possibly the US.

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 November 24. Iranian Deputy Foreign Minister Abbas Araghchi said last week that Tehran is already talking to the US 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 sceptics in US 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,” says Gary Samore, who left the US team negotiating with Iran last year. “It is likely to be strongly resisted both in Washington and Tehran.”

For the US administration, any extension may need to include persuading opponents in the US Senate that it’s in Washington’s interests. The prospect that Republicans could win a majority in the Senate in November 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 November 24 may sway Khamenei, who has frequently expressed distrust of US aims at the talks even while backing the process up to now.

Senate sceptics are worried that any deal will relieve sanctions pressure on Iran without making a sizeable 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 programmes for insufficient economic advantage.