British Foreign Secretary Boris Johnson held almost an hour of talks with Iranian President Hassan Rouhani on Sunday after flying to Tehran to seek the release of a jailed British-Iranian aid worker.

"Both spoke forthrightly about the obstacles in the relationship and agreed on the need to make progress in all areas," said a spokeswoman for Britain's Foreign Office after Johnson concluded what was only the third visit to Iran by a British foreign minister in the past 14 years.

The Foreign Office confirmed Johnson had raised "consular cases of dual nationals" during talks. These cases include Nazanin Zaghari-Ratcliffe, who Britain says was visiting family on holiday in April 2016 when she was jailed by Iran for attempting to overthrow the government.

The woman's husband later told Sky News that a court appearance scheduled in Iran for Sunday had been postponed. "I think I am very optimistic today," Richard Ratcliffe said.

He added that he hoped his wife would be home before Christmas but cautioned that there could still be setbacks.

"Without doubt having the foreign secretary there was a big thing. Without doubt the court case not happening is a big thing. There may be a number of big things that have to happen before she's home, but ... as I sit here I am a lot more optimistic than I was."

Iranian state television had reported that "bilateral relations, the nuclear deal and regional developments made up the axis of the talks", between the president and Johnson.

TWO-DAY VISIT

The case of Zaghari-Ratcliffe has taken on domestic political importance after Johnson said last month that she had been teaching journalists in Iran, which her employer denies. Johnson later apologized. Opponents have called for him to resign if his comments lead to her serving longer in prison.

Johnson met Ali Akbar Salehi, head of Iran's Atomic Energy Organization earlier on Sunday and had talks with his Iranian counterpart Mohammad Javad Zarif on Saturday.

The two-day visit took place against a complex backdrop of historical, regional and bilateral tensions.

"It has been a worthwhile visit and we leave with a sense that both sides want to keep up the momentum to resolve the difficult issues in the bilateral relationship and preserve the nuclear deal," the Foreign Office spokeswoman added.

International sanctions against Iran have only recently been lifted as part of the 2015 multilateral nuclear deal to curb Tehran's disputed uranium enrichment program.

That deal is under threat after U.S. President Donald Trump decided to decertify Iran's compliance with its terms. Johnson told Zarif he believed the deal should be fully implemented.

Zaghari-Ratcliffe is not the only dual national being held in Iran, but has become the most high profile case.

A project manager with the Thomson Reuters Foundation, she was sentenced to five years in prison after being convicted by an Iranian court of plotting to overthrow the clerical establishment. She denies the charges.

The Thomson Reuters Foundation is a charity organization that is independent of Thomson Reuters and operates independently of Reuters News. It says Zaghari-Ratcliffe had been on holiday and had not been teaching journalism in Iran.