The foreign ministers of Iran, the US, Britain, China, France and Germany are hoping to reach a framework nuclear deal with Tehran. The deadline ends at midnight on March 31.
Representatives of Iran and permanent members of the Security Council plus Germany were expected to reach an agreement on Tuesday following nearly one and a half years of talks to convince Tehran not to make nuclear weapons.
"There still remain some difficult issues… We are trying very hard to work those through," US Secretary of State John Kerry, who has been in Lausanne since Wednesday, told CNN.
Kerry met foreign ministers from France, Britain, China and Germany first thing on Tuesday. Russian foreign minister Sergei Lavrov left the talks on Monday and would return only if there was a "realistic" chance of a pact, his spokeswoman said.
Final pact a long way off
The deal, which is to reach its final form on June 30, foresees Iran scaling back its nuclear program. The issues being negotiated include the future size of Iran's uranium enrichment capacity and reduction of its nuclear stockpiles.
The ultimate goal is to find a way to ensure that for the next 10 years, Iran is at least one year away from producing fissile material for an atomic weapon.
Tehran has denied using its nuclear reactors to build weapons and maintains that its program is for peaceful purposes only.
A final agreement, which aims to end a standoff between the West and Iran for nearly 12 years, is being held up because of Tehran's wish to continue nuclear research and development, and its demand to end UN sanctions in exchange for temporary limits to its atomic program.
"There will be no agreement if the sanctions issue cannot be resolved," Majid Takhteravanchi, Iran's nuclear negotiator told the Pars news agency.
A lasting deal could still be a long way off if the two sides disagree on technical aspects of the agreement.
Negotiations have also been marred due to Israel's fears that a nuclear agreement between Iran and the West could jeopardize its safety.
mg/lw (Reuters, AFP)