WASHINGTON — As talks on Iran’s nuclear program resume Thursday, the top US negotiator with Iran will participate in a trilateral meeting with her Iranian and EU counterparts.

Both Western and Iranian diplomats have suggested that the implementation of the interim agreement outlined in the Joint Plan of Action, or JPA, could be initiated as early as January 20, but a few major stumbling blocks still lie in the way of a workable interim deal.

After weeks of “technical” talks to iron out disagreements surrounding clauses of the November 24 deal on the Iranian nuclear program, Iranian media reported Wednesday that Washington’s chief negotiator on the topic — Undersecretary for Political Affairs Wendy Sherman — may participate in a trilateral meeting with Iran’s Deputy Foreign Minister for Legal and International Affairs Abbas Araqchi and European External Action Service Deputy Secretary General for Political Affairs Helga Schmid. The meeting was later confirmed by the US.

Thursday’s summit marks the first meeting of the political-level negotiators in the new year, although technical negotiators have already resumed talks after a holiday break. Both Iranian and Western officials have confirmed that the sides have set January 20 as a start date for the interim agreement.

Earlier this week, Araqchi said that if the upcoming talks resolve the existing differences, the start date for the six-month-period outlined in the agreement can be determined.

Sherman’s participation was first revealed by Iran’s PressTV, when it reported that Araqchi said that the three may meet in trilateral talks in Geneva.

The State Department on Wednesday issued a statement confirming that “Under Secretary Sherman will hold meetings with [Schmid] and with [Araghchi] to discuss the implementation of the Joint Plan of Action agreed to by the P5+1 and Iran.”

The talks are scheduled to be a one-day affair, as Sherman is expected to be in Moscow Friday to discuss Syrian peace talks with her Russian counterparts.

On Wednesday, State Department Spokeswoman Jen Psaki said that “there are just a few remaining issues” that need to be negotiated before the announcement of an implementation agreement.

But the “few remaining issues” might prove to be more than a few days’ worth of stumbling blocks.

Unnamed “Western” diplomats told Reuters news service Wednesday that a major dispute has arisen over the development and installation of so-called “next generation” centrifuges. The centrifuges, which allow Iran to more efficiently enrich uranium to weapons-grade levels.

According to the diplomat, the “next-generation” centrifuges proved to be one of the key factors during the previous talks which concluded on December 21. Following that session, the website Al-Monitor quoted former US official Jofi Joseph as saying that “what may be happening here is that Iran has notified the P5+1 that it plans to install additional IR-2M centrifuges at the Pilot Fuel Enrichment Facility at Natanz where it has historically conducted centrifuge research and development.”

Iran has announced that it is testing new centrifuges that analysts say may even be more advanced than the IR-2Ms. Under the nuclear deal, Iran may not install any new centrifuges unless they are replacing damaged ones.

In a meeting this week with British members of Parliament, Israeli Foreign Minister Avigdor Liberman said that the Iranian announcement of the installation of new centrifuges with five times the production capacity of the earlier generation of centrifuges negates the spirit of the agreement signed in Geneva, and proves that the sole purpose of the Iranians at this stage is to win time in order to achieve their goal of obtaining nuclear weapons.

Liberman told the MPs that he expects the powers conducting the talks not to allow them to have it both ways.