While Trump has said he prefers to solve the crisis through diplomacy, he has also said he is considering a limited strike on Iran to pressure its leaders to accept a deal.

The president, however, has done little to explain what he is demanding in the negotiations and why there could be the need to take military action now, eight months after the US bombed Iranian nuclear facilities during a war between Israel and Iran.

Iran has rejected the US demand to stop the enrichment of uranium in its territory, but there have been indications that it is prepared to offer some concessions about its nuclear programme.

Iran’s proposals have not been made public, but the discussions in Geneva could include the creation of a regional consortium for uranium enrichment, which has been raised in previous negotiations, as well as ideas about what to do with Iran’s roughly 400kg (880lb) stockpile of highly enriched uranium and verification and monitoring mechanisms.

In return, Iran expects the lifting of sanctions that have crippled its economy. Opponents of the regime say any relief would give the clerical rulers a lifeline.

But it remains unclear which conditions Trump could find acceptable for a deal. Iran has already rejected discussing limits to the country’s ballistic missile programme and ending its support for proxies in the region – an alliance Tehran calls the “Axis of Resistance” that includes Hamas in Gaza, Hezbollah in Lebanon, militias in Iraq, and the Houthis in Yemen.

Reports in US media, quoting unnamed administration officials, have suggested that Trump was considering an initial strike in the coming days on Iran’s Revolutionary Guards or nuclear sites to pressure the country’s leaders. If negotiations failed, according to the reports, the president might go as far as ordering a campaign with the aim of toppling the Iranian Supreme Leader, Ayatollah Ali Khamenei.

The Chairman of the Joint Chiefs of Staff is also said to have warned that strikes against Iran could be risky, potentially drawing the US into a prolonged conflict, although Trump has insisted that Gen Dan Caine believes it would be “easily won”.

Iran, meanwhile, has threatened to respond to any attack by striking American military assets in the Middle East and Israel.

US-allied countries in the region are concerned that an attack on Iran could lead to a wider conflict, and have warned that air power alone will not be able to change the country’s leadership.

Israeli Prime Minister Benjamin Netanyahu, however, has warned against a deal that does not include Iran’s ballistic missiles and its proxies. Netanyahu has long described Iran as a key threat for Israel, and a source of instability in the region.

Analysts believe that the prime minister, who visited the White House earlier this month, may be pushing for a campaign with the goal of toppling the Iranian regime.

The US has the world’s second-largest nuclear arsenal. Israel is also believed to have nuclear weapons, although it neither confirms nor denies this.

Ahead of the State of the Union, Secretary of State Marco Rubio delivered a classified briefing to the so-called “gang of eight”, composed of the leaders of both parties in the Senate and House of Representatives and the chairs and ranking members of the intelligence committees of both chambers.

Following the briefing, Chuck Schumer, the Senate minority leader, gave a brief statement, saying: “This is serious, and the administration has to make its case to the American people.”