Iran’s Foreign Minister, Mohammad Javad Zarif, on Wednesday played down the chances of reaching a nuclear agreement during talks under way in Switzerland, AFP reported.

Zarif, who has been in talks in Switzerland with U.S. Secretary of State John Kerry since Monday, said other foreign ministers from world powers involved in the negotiations were unlikely to join them for now.

The arrival of the foreign ministers of Russia, China, Britain, France and Germany in Lausanne could indicate that a long-elusive deal might be at hand.

“I don’t think their presence will be needed in this round,” Zarif was quoted as having told Iranian state media from the Swiss lakeside city.

“When the solutions are found and we approach a deal, then all the foreign ministers of the negotiating parties should come,” he added.

As a result the negotiations will likely have to continue into next week or resume then after a break.

The talks are geared towards turning an interim 2013 deal into a permanent agreement.

Under the interim deal, Iran committed to limit its uranium enrichment to five percent and is gradually winning access to $4.2 billion of its oil revenues frozen abroad and some other sanctions relief.

Talks to reach a permanent deal have continuously stalled and two deadlines for a final deal have been missed. Experts say that the new deadline — March 31 for a framework deal, July 1 for the full deal — has to be met.

It is however far from certain that the sides will manage to get a deal, AFP noted, with both sides warning of disagreements on key issues, principally the future size of Iran’s program and the timing of easing sanctions.

On Tuesday the White House said the chances of such a deal are 50/50 “at best” with “some of the most difficult issues… yet to be resolved.”

Zarif said Wednesday that “there are differences and we are trying to reduce them”.

On Tuesday, Iranian nuclear chief Ali Akbar Salehi, also in Lausanne along with U.S. Energy Secretary Ernest Moniz, had said “90 percent of the technical issues” have been agreed.

On Wednesday he said that “progress” had been made and that he was “optimistic”. It was unclear whether negotiators would have to return next week, he added.

“We don’t know yet, we still have two days to go,” he told reporters as he strolled by Lake Geneva.

He also said that the “framework” being targeted by March 31 would cover “general issues”.