WASHINGTON (WASHINGTON POST) - On Sunday's Face The Nation programme, Kim Darroch offered fans of the Iran deal reason to hope.

The British ambassador to the United States told host Margaret Brennan that he believes the 2015 accord will be saved.

President Donald Trump is famously opposed to the agreement, which offered Iran relief from major economic sanctions in exchange for a curb on nuclear programmes.

Trump has called it the worst deal in US history, once suggesting it was so bad that "there has to be something else going on". "Who would make that deal?" he asked in 2016.

As presidential candidate, Trump told voters he would pull out of the agreement. As president, he has been slightly more measured. Last October, he officially disavowed the deal, though he stopped short of terminating it. Instead, he passed the buck to Congress, giving them the power to reimpose sanctions - or not.

Now, though, he is considering whether to restore US sanctions against the country. If that happens, it will put all of the treaty's signatories in a tricky position. It will also make it much harder to keep Iran from developing nuclear weapons.

By all accounts, Iran has complied with the deal. But Trump says the deal is far too weak to really constrain the country's nuclear ambitions.

Among his concerns: The regulations on Iran expire at a certain point. These "sunset clauses" lift restrictions on some Iranian nuclear activities after a decade.

The treaty does not prohibit the testing of ballistic missiles, which Iran has continued to do.

The Trump administration has also criticised Iran for its support of militant groups such as Hizbollah and Hamas, arguing that the country is destabilising the region.

On Sunday, Darroch said that Britain has some ideas for addressing Trump's concerns.

"We think that we can find some language, produce some action that meets the President's concerns," he said, noting that his team was working closely with France and Germany, other advocates of the deal.

Darroch also told Brennan that Trump and British Prime Minister Theresa May spoke on Saturday, and that Trump told May that "a final decision hasn't yet been taken".

Darroch said he had personally lobbied national security adviser John Bolton as well. (Bolton is no great fan of Iran, but has said he thinks the United States should stay in the accord for now.)

It is not clear exactly what those fixes will look like. In the past, European negotiators have said that there are opportunities to tweak the deal so that missile tests are limited and banned.

They are also open to pushing Iran to agree to give inspectors unfettered access to Iranian military bases. It is unclear whether Iran would agree to those terms.

"We think it's a good deal," Darroch said. "We have been talking at senior official level to the administration with our French and German colleagues for several weeks now. We think we're making progress. We haven't got there yet. We have a few days left to see if we can find a way through."

Darroch's interview came just days before British Foreign Secretary Boris Johnson flies to Washington for two days of talks with officials. His aim is to salvage the accord ahead of Trump's deadline on Saturday.

Last month, French President Emmanuel Macron made an impassioned case to Trump and in a talk to a joint session of Congress against scrapping the deal.

But on the last day of his visit, Macron told reporters that he did not think he had succeeded.

"My view is... that he will get rid of this deal on his own, for domestic reasons," Macron said at the end of a three-day visit, according to the BBC.