Marathon talks to draw up the outlines of a landmark Iran nuclear deal by March 31 looked set to go down to the wire as Tehran's foreign minister played down chances of finishing the job this week.

Mohammad Javad Zarif, in talks in Switzerland with US 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 - joining their political directors - could indicate that a long-elusive deal might be at hand.

"I don't think their presence will be needed in this round," Zarif 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 said.

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

Al Jazeera's James Bays, reporting form Lausanne, said many issues were still undecided.

"Everyone you speak to here is saying that progress is taking place. But I cannot tell you whether there will be a deal. We're getting all our information from snatched conversations as all talks are taking place in closed rooms.

"One Iranian delegate told us that when they do their internal deliberations, they actually go for a walk because they are worried that the rooms where the talks take place may well be bugged."

Iran and the six powers have been seeking in months of talks to transform an interim deal struck in November 2013 into a lasting accord that they hope will convince the world that Tehran is not about to develop nuclear weapons.

Such an agreement would involve Iran scaling down its nuclear activities to within strict limits in exchange for relief from painful sanctions after 12 years of rising tensions over its atomic programme.

Two earlier target dates last July and then again in November were missed, but experts say that the new deadline - March 31 for a framework deal, July 1 for the full deal - has to be met.

Differences

It is, however, far from certain that they will manage to get a deal, with both sides warning of disagreements on key issues, principally the future size of Iran's programme 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 on 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 US Energy Secretary Ernest Moniz, had said "90 percent of the technical issues" had been agreed.

Technical aspects are, however, only part of what would be a highly complex "Rubik's Cube" agreement and Washington has consistently driven home that all the interlocking parts have to fit together.

Salehi said on Wednesday that "progress" had been made and that he was "optimistic". It was unclear whether negotiators would have to return next week, he said.

"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".

Source: Al Jazeera And Agencies