Donald Trump has told British officials he is not seeking a military confrontation with Iran and is instead aiming for direct talks with Tehran over his plan to negotiate and broaden the country’s nuclear deal.

Despite the assurances, British officials remain nervous the US president may have only 30 days before Iran takes irreversible steps to forgo the agreement.

The assurance that Trump is not seeking war with Iran was made by US officials to British counterparts in talks surrounding the president’s three-day state visit to the UK. They also claimed the US policy of sending extra troops and an aircraft carrier to the region had acted as a deterrent.

Britain, at odds with Washington over how to handle Iran, acknowledges the US policy of applying maximum economic pressure is taking a huge toll on Iran and has pushed the country close to insolvency. Officials also said Javad Zarif, the Iranian foreign minister, had a mandate to determine whether the conditions for talks could be reached.

But with Iran set to take further steps within a month to break out of the deal – known as the Joint Comprehensive Plan for Action - the UK remains nervous the two sides do not have long to reach an agreement on the terms for talks. Further actions by Tehran are likely to lead to a declaration by the International Atomic Energy Authority that Iran is not in compliance with the deal, ratcheting up tensions.

Iran is hoping that a two-day visit to Tehran next week by the Japanese prime minister, Shinzo Abe, will be the moment when messages from the US are delivered, setting out the terms for talks.

The Iranian deputy foreign minister, Abbas Araghchi, this week welcomed Japanese mediation. “Unfortunately tension is increasing and we hope that [the Japanese] prime minister’s visit to Tehran would help to ease tensions in the region,” he said. He added that, as a ally of Washington, Japan will probably be able to make the US understand the situation.

Abe is scheduled to meet Iranian leaders, including the leader of the Islamic revolution, Ayatollah Ali Khamenei, during his visit starting next Wednesday. Abe has met the president of Iran, Hassan Rouhani, six times since he was appointed prime minister, and Japan, an energy importer, has not endorsed Trump’s contentious move to recognise Jerusalem as the capital of Israel. Japan, however, has no history of mediation in the Middle East.

Tehran will insist some US sanctions are lifted as a precondition for talks, and is willing to offer the release of a number of US political prisoners as a sign of goodwill. It is not clear if the terms would be enough for Trump to agree to hold talks. The US secretary of state, Mike Pompeo, said this week Washington was willing to talk without preconditions. Within Iran, the issue of whether to seek talks or simply hold out until Trump is defeated in the presidential elections is a matter for open political debate.

Trump himself has said on his trip that he is prepared to talk to Rouhani, but added “there’s always a chance” that the US would need to take military action. “I’d much rather talk,” said Trump, in an interview with Piers Morgan on Good Morning Britain, carried out on Tuesday evening.

Plans for the US to put evidence to the UN security council setting out direct Iranian involvement in an attack on four empty oil tankers off the coast of the United Arab Emirates may be put on hold in a sign that the US is willing to lower the temperature and see if the offer of talks can be reciprocated.

The national security adviser, John Bolton, this week raised the prospect of US officials putting the largely Mossad-sourced evidence of Iranian involvement in the tanker attacks to the security council. Bolton said the Islamic Revolutionary Guards Corps was “almost certainly” behind the attack on the shipping in Fujairah, and that he saw it as a warning shot for what the Iranians might do in extremis to damage oil shipping through the Straits of Hormuz. Iran denied any involvement in the attack.

Trump pulled out of the nuclear deal a year ago, imposed sweeping sanctions on Iran, and since November has tried to impose a ban on all Iranian oil exports – the lifeblood of the country’s economy, which normally exports 2.5m barrels a day, but is now down to 400,000. These export levels could bring the Iranian government close to insolvency.

Europe, to Iran’s fury, has proved incapable of protecting trade with Tehran in the face of the threat of US sanctions. EU firms, especially those that trade in American dollars, have not been willing to risk US sanctions. China, India and Pakistan have not resumed oil imports, but the EU is taking the bulk of the diplomatic flak in Tehran for failing to stand up to the US.

Iranians’ hopes of waiting for the Democrats to be in charge are looking increasingly unviable. In turn, Washington may not want to try to jump-start talks in 2021 with a freshly elected Iranian hardliner.

Meanwhile, British officials fear that if talks do not start soon, the threat of an Iranian-US conflict developing by accident could come from Yemen.

Iran is increasingly backing Houthi rebels with sophisticated drones capable of attacking Saudi cities, shipping and territory. The Houthis are at war with Saudi Arabia over the kingdom’s support for President Abdrabbuh Mansur Hadi, a leader that the Houthis deem as a puppet of Riyadh. Britain has been privately urging the Saudis to reach a settlement in Yemen, fearing the rebels, increasingly dependent on Iran, will launch an attack on Saudi cities that could lead to a regional conflagration.