LAUSANNE, Switzerland - Iranian and Western diplomats gave dueling accounts of what is needed to reach a nuclear accord in the 48 hours before their deadline, with each side saying the other must make tough choices.

Foreign ministers from six world powers and Iran will meet Monday morning in Lausanne. Diplomats remain divided over the pace of easing sanctions on the Iran, and the limits to be imposed on its nuclear program.

The "other side must make serious decisions," Iran's Deputy Foreign Minister Abbas Araghchi told reporters late Sunday in the Beau Rivage Palace Hotel. At the same moment, Philip Hammond, Britain's foreign minister, was telling another group outside the hotel that "Iran has to take a deep breath and take tough decisions."

A framework accord by the end of March would be a major step toward ending Iran's economic isolation. Failure would be a blow to President Obama, who has backed the talks despite domestic opposition, and increase the risk of military action by the U.S. or Israel to prevent Iran from getting nuclear weapons.

A new wrinkle emerged late Sunday as Araghchi contradicted earlier reports that Iran, which says its nuclear program is for peaceful purposes, was prepared to ship out its enriched uranium stockpile to a third country. "We don't have the intention to ship our material abroad, but there are other solutions to create trust," Araghchi said.

A day earlier, some diplomats had put the chances of reaching a deal at more than 50 percent. German Foreign Minister Frank-Walter Steinmeier said Sunday there had been "both progress and backsliding in the last few hours."

Russian Foreign Minister Sergei Lavrov arrived late Sunday to join the talks and met with Secretary of State John Kerry, who has canceled a Monday engagement in Boston. Their French and German counterparts, Laurent Fabius and Steinmeier, also cleared their schedules to remain at the negotiations, European officials said.

Foreign ministers and other representatives of negotiators have said there is a chance of succeeding by the deadline despite obstacles. White House spokesman Josh Earnest said it was up to Iran to make that happen. By accepting the restrictions, the Iranians would "live up to their rhetoric that they are not trying to acquire a nuclear weapon," he said in Washington on ABC's This Week.

Sen. Bob Menendez of New Jersey, the top Democrat on the Senate Foreign Relations Committee, said Sunday that he has "real concerns" over the talks and would not support any deal that leaves Iran a "threshold nuclear" state. He is cosponsoring a bill with the committee's chairman, Sen. Bob Corker (R., Tenn.), that would allow the Congress to any deal that emerges. The White House has said President Obama would veto the proposed bill, which would require the administration to wait 60 days before suspending any sanctions against Iran.