French Foreign Minister Laurent Fabius, who arrived late Wednesday to join the Iran nuclear talks, says the negotiations are in the final but most difficult stage, Press TV reported.
"We are a few meters... from the finishing line, but we are well aware that the final meters are the hardest," AFP quoted Fabius as saying in the Swiss city of Lausanne on Wednesday.
Iran and the P5+1 group of world powers, which includes the U.S., China, France, Russia, the UK, plus Germany, set March 31 for negotiators to reach an outline of a much sought after deal on Iran's nuclear program.
Negotiators have been engaged in marathon talks in Lausanne to try to reach the deal ahead of an end of June deadline for a final accord.
Two previous deadlines for a deal have passed as negotiators seek to curb Iran's nuclear program in exchange for sanctions relief.
Tehran has long maintained that its nuclear program is solely for peaceful civilian purposes but world powers are suspicious that the program could potentially be used for military purposes.