MONTREUX, Switzerland — US officials sought to tamp down expectations of a substantial preliminary nuclear deal with Iran by the March deadline Wednesday while working to move past the political dust kicked up by Prime Minister Benjamin Netanyahu of Israel’s criticism of an emerging agreement’s contours.

Secretary of State John F. Kerry said Washington was well aware of the potential nuclear danger Iran poses to the region and will endorse only an agreement that crimps Tehran’s ability to make atomic arms.

‘‘We continue to be focused on reaching a good deal, the right deal, that closes off any paths that Iran could have toward fissile material for a weapon and that protects the world from the enormous threat that we all know a nuclear-armed Iran would pose,’’ Kerry told reporters at the end of meetings with Foreign Minister Mohammad Javad Zarif of Iran.


The sides hope to have a progress report by late March allowing them to finesse details into a final pact by June. But a senior US official appeared to walk back from the significance of that first stage, describing it as only ‘‘an understanding that’s going to have to be filled out with lots of detail’’ by the June final target date.

The official’s comments could be an attempt to stretch the interpretation of what should be achieved by March.

Justifying an extension of the talks on Nov. 24, Foreign Secretary Philip Hammond of Britain — one of five powers backing the United States at the talks — said he expected ‘‘an agreement on substance’’ by March. Western and Iranian negotiators said they would use the time between March and June only ‘‘if necessary ... to finalize any possible remaining technical and drafting work.’’

The US official, who demanded anonymity in line with State Department rules, said President Obama will make a call on whether to continue into June once he sees the March assessment from US negotiators.


Playing down the prospects of any lasting damage to US- Israeli ties caused by Netanyahu’s speech to Congress Tuesday, the US official said senior Israeli officials will be briefed by secure phone by top US negotiators on the latest round.

Still, the Netanyahu speech is likely to embolden critics in Congress who fear the United States could accept terms too lenient on Iran. He told Congress Tuesday that the agreement taking shape is dangerous and would allow Iran the ability to develop nuclear weapons.

Last week, senators introduced legislation to give Congress a say over a deal, and Republicans are trying to get it passed as the talks continue.

The American public appears to support more sanctions. A new AP-GfK poll shows more than 6 in 10 Americans say they favor Congress instituting new sanctions against Iran, while only 7 percent say they are opposed. Another quarter of Americans say they are neither in favor nor opposed. The poll had a margin of error of 3.5 percentage points.

Kerry planned to meet with Arab Gulf state allies in Riyadh Thursday.