The US and Iranian foreign ministers began a third day of talks over Iran's nuclear program on Wednesday, just hours after Israeli Prime Minister Benjamin Netanyahu had warned that the deal being negotiated was a serious mistake.
US Secretary of State John Kerry and Iran's Mohammad Javad Zarif resumed their discussions in the Swiss lakeside town of Montreux, hoping to work out a framework deal by late March.
However, Netanyahu's controversial speech to the US Congress on Tuesday, where he harshly criticised the diplomatic efforts to resolve the dispute, will make it harder for the Obama administration to sell the potential deal back home.
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 US interests at risk.
US 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, US 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.