The U.S. and Iranian foreign ministers wrapped up three days of talks over Iran's nuclear programme, a day after Israeli Prime Minister Benjamin Netanyahu said the deal being negotiated was a serious mistake.
.S. Secretary of State John Kerry and Iran's Mohammad Javad Zarif have negotiated for more than 10 hours since Monday in the Swiss lakeside town of Montreux, hoping to work out a framework deal by late March.
"We have made some progress but have a lot of challenges yet ahead," a senior U.S. State Department official told reporters traveling with Kerry.
"The bottom line here is that (there is) no deal to announce to anybody today, but very intense, hard work, some progress, but tough challenges yet to be resolved," the official said.
"We expect that we (and the Iranians) will regroup bilaterally, with the European Union present as well, on the 15th of March, location to be confirmed but most likely Geneva."
Asked if he thought they had made progress, Zarif told reporters: "We have, but a lot of work remains."
However, Netanyahu's controversial speech to the U.S. Congress on Tuesday, where he harshly criticised the diplomatic efforts to resolve the dispute, may make it harder for the Obama administration to sell the potential deal back home.
U.S. negotiator Wendy Sherman will brief Israel soon on the talks and Kerry will meet the foreign ministers of Britain, France and Germany in Paris on Saturday, the senior U.S. official said.
Netanyahu argued that rather than preventing Iran from acquiring nuclear arms, a deal would "all but guarantee" that it would one day get the atomic bomb, putting Israel, the wider region and U.S. interests at risk.
U.S. President Barack Obama responded within hours saying that Netanyahu had offered no "viable alternatives" to the current course of negotiations.
Iran and world powers are trying to put a framework agreement in place by the end of the month, despite the misgivings of Israel, U.S. congressional Republicans and some Gulf Arab states. Such an accord would be followed by a comprehensive agreement to be completed by the end of June.
The aim of the negotiations is to persuade Iran to restrain its nuclear program in exchange for relief from sanctions that have crippled the oil exporter's economy.
The United States and some of its allies, notably Israel, suspect Iran of using its civil nuclear program as a cover to develop a nuclear weapons capability. Iran denies this, saying it is for peaceful purposes such as generating electricity.