Vice President JD Vance will not head to Switzerland Thursday evening for the first round of planned technical nuclear talks with Iran, his office announced.

The trek to Switzerland was already in flux, the veep had previously admitted, as his team worked to iron out the logistics and figure out whether or not the Iranians would participate. The technical negotiations were outlined in a memorandum of understanding between the US and Iran that was finalized this week.

“As the Vice President said at his press conference, the plans for the upcoming technical talks have not been finalized, and the U.S. delegation has been prepared to depart at the first available opportunity,” a White House spokesperson said in a statement.

“[T]he logistics of these negotiations have never been simple or predictable,” the spokesperson added. “As of now, the Vice President is not departing tonight. We look forward to beginning technical talks as soon as possible.”

Initially, a formal signing ceremony for the MOU with Iran was expected to take place on Friday. An official agenda or schedule hasn’t been disseminated.

It’s not immediately clear what logistical snarls caused the delay, but Vance implied that the Iranians may have a difficult time leaving their mountainous country.

“We think these technical negotiations are going to start sometime this weekend; that’s still the plan, but that could change because it’s not an easy country, Iran, to get out of, and so we’re trying to figure out exactly when that’s going to happen,” Vance said during the White House press briefing Thursday.

“I suspect this weekend, but I’m not sure.” 

Under the MOU — which was electronically signed Sunday by Vance, then by President Trump on Wednesday in France — both the US and Iran agreed to technical talks over a 60-day period to hash out the details of the Iranian regime’s concessions on its nuclear program.

The talks are expected to include specifics of how Tehran will address its stockpile of enriched uranium and other, more granular, details of the broader peace agreement.