The talks between the P5+1 world powers group and Iran continued beyond the March 31 deadline on Tuesday night.
US State Department spokesperson Marie Harf announced there had been "enough progress in the last days to merit staying until Wednesday" but that there were "several difficult issues still remaining."
Despite the lingering disagreement, the assessment in Israel is that some form of a framework "understanding" will emerge from this round of talks in Lausanne which will enable the sides to continue negotiating over a more detailed deal towards the next deadline at the end of June.
Few details have emerged from the prolonged meetings between the sides but the participation of the foreign ministers of the involved nations, including Britain's Philip Hammond, who was the last of the ministers to arrive at Lausanne, is an indication that some form of agreement is expected.
One of the core disputes is known to be over what form that agreement should take.
Some form of framework 'understanding' will emerge
The Iranians favour the announcement of a general "understanding" with a written agreement only at the end of the process, in three months' time.
The Americans, however, have insisted on having at least the points of agreement included in a written document, as the US Congress is planning to debate legislation for new sanctions on Iran in the next few weeks.
While most of the diplomats in Lausanne refused to speculate on the chances of reaching a deal, Russian Foreign Minister Sergei Lavrov said that "prospects for this round of negotiations were not bad and I would even say good".
A senior Israeli official said this week that the immediate implication of a completed deal will be increased Israeli surveillance of Iran's nuclear installations and the threat of a military attack if there is proof that it is in breach of the agreement.
Other known disagreements include the Iranian refusal to ship most of the uranium it has already enriched out of the country. In the details of a provisional agreement leaked from previous rounds of the talks, the Iranians had agreed for the enriched uranium to be transferred to Russia.
In addition, there are still disagreements on the order and pace of sanctions relief. The Iranians urge a speedy removal of the United Nations sanctions, while the Americans prefer to first remove the more flexible European Union sanctions, as it will be very difficult to obtain a UN resolution on renewed sanctions if Iran reneges on an agreement.
The sides are also far apart on the issue of nuclear research and development during the ten years in which increased inspections on Iran's nuclear programme are supposed to take place.
Another issue that remains unclear is whether the "possible military dimensions" of the Iranian nuclear programme - the long-range missiles and other necessary components of a nuclear weapon, which Iran has refused so far to discuss - will be covered in any way in the agreement.
Despite the delays in the talks, the Israeli leadership has come to terms with the idea that a deal will probably be reached.
At the swearing-in of the new Knesset on Tuesday afternoon, Prime Minister Benjamin Netanyahu said: "The agreement which is forming now in Lausanne is paving Iran's way to a nuclear weapon."
While the Americans have insisted that the terms of the deal will ensure that it will take Iran at least a year to "break out" and build a nuclear weapon, Mr Netanyahu said that "Iran's breakout time for a nuclear weapon won't be years as we were told originally but is shrinking to a year, perhaps even less."
