U.S. Secretary of State John Kerry will travel to Vienna later Thursday to join high-level nuclear negotiations with Iran as a deadline for an agreement fast approaches.

State Department spokeswoman Jen Psaki said Kerry would be going to the Austrian capital from Paris to “check in” on the talks. It was not yet determined how long he would stay in Vienna, leaving open the possibility that he might not remain until Monday’s deadline for a deal. Kerry is to meet with the U.S. negotiating team in Vienna late Thursday before scheduling meetings with other participants.

Kerry had been expected to join the Vienna negotiations, but the timing of his arrival at the talks had been uncertain until shortly after he arrived in Paris for talks with the Saudi and French foreign ministers after two days of similar meetings in London with his British and Omani counterparts. Kerry is to hold a news conference in Paris after seeing French Foreign Minister Laurent Fabius and before departing for Vienna.

With Monday’s deadline for a deal looming, Kerry has embarked on a frenzy of high-stakes diplomacy in a last-minute push to secure an agreement — or at least prevent the process from collapsing after talks were already extended once.

Senior negotiators in Vienna have spent three days racing against the clock to forge a pact over the next five days that would prevent Iran from reaching the capability to produce atomic weapons.

Despite Kerry’s efforts, though, signs increasingly pointed to the Nov. 24 deadline passing without a deal and the negotiations being extended a second time.

In London on Tuesday and Wednesday, Kerry met with Foreign Minister Yusuf bin Alawi of Oman, a key bridge between Washington and Tehran, a senior U.S. official said. Bin Alawi was in Tehran last weekend.

Oman is not party to the negotiations among Iran, the U.S., Britain, China, France, Russia, the European Union and Germany. But it is unique among the Gulf Arab states for the close ties it maintains with Iran, having hosted high-level nuclear talks earlier this month and served as the site of secret U.S.-Iranian gatherings dating back to 2012. Those earlier discussions laid the groundwork for an interim nuclear agreement reached a year ago, which the so-called P5+1 countries now hope to cement with a comprehensive accord in Vienna.

In Washington on Wednesday, President Barack Obama’s nominee to be Kerry’s deputy at the State Department said he believed it would be difficult to meet the deadline.

“It’s not impossible,” said Tony Blinken, currently Obama’s deputy national security adviser. “It depends entirely on whether Iran is willing to take steps it must take to convince us, to convince our partners that its program would be for entirely peaceful purposes. As we speak, we’re not there.”

Peter Wittig, Germany’s ambassador to the U.S., wouldn’t rule out an extension and said a nuclear deal could lead to better relations between Iran and world powers on regional crises in Syria and Lebanon.

“If these negotiations fail, there won’t be any winners,” Wittig told reporters in Washington.

Kerry’s meetings with Fabius and Saudi Foreign Minister Saud al-Faisal are considered critical because French objections last year delayed the adoption of an interim agreement by several weeks, and Saudi Arabia remains deeply concerned about the potential for its archrival Iran to win concessions from the West.

The Obama administration also is trying to satisfy the concerns of Republican and many Democratic lawmakers at home.

Republican senators sent a letter to the White House on Wednesday urging the administration against trying to circumvent Congress in any deal with Iran. “Unless the White House genuinely engages with Congress, we see no way that any agreement consisting of your administration’s current proposals to Iran will endure,” said the letter, which was signed by all 45 Senate Republicans.

In a twist, many in Congress who previously opposed further extensions of talks with Iran now see that route as a preferable to an agreement that doesn’t do enough to cut off possible Iranian pathways toward a nuclear bomb.

Republicans in particular want more time so they can attempt to pass new sanctions legislation that would pressure Iran into greater concessions. Their plan is to bring up a package of conditional penalties after January, when they take the Senate majority, according to GOP Senate aides who weren’t authorized to speak publicly on the matter and demanded anonymity.

Some Democrats are on board with that effort, though Obama has threatened to veto any new sanctions threatening the diplomacy.

Even Israel, which has been among the most hostile to the West’s diplomatic overtures toward Tehran, is suggesting it is amenable to an extension. The option would allow time for a better agreement to be negotiated through additional economic sanctions on Iran, a senior Israeli official said.

(AP)