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.
Iranian state television had reported that "bilateral relations, the nuclear deal and regional developments made up the axis of the talks," with the president.
Johnson met Ali Akbar Salehi, head of Iran's Atomic Energy Organisation earlier on Sunday.
"In both meetings the Foreign Secretary discussed the full range of regional and bilateral issues, including banking matters and our concerns about the consular cases of dual nationals," the Foreign Office spokeswoman said.
On Saturday Johnson had talks with his Iranian counterpart Mohammad Javad Zarif about "consular cases of dual nationals" such as Nazanin Zaghari-Ratcliffe, who Britain says was visiting family on holiday when she was jailed by Iran for attempting to overthrow the government.
The case has taken on domestic political importance after Johnson said last month that Zaghari-Ratcliffe trained journalists, which her employer denies. Johnson later apologised. Opponents have called for him to resign if his comments lead to her serving longer in prison.
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 programme.
The Foreign Office did not mention Zaghari-Ratcliffe by name, although Johnson has vowed to leave "no stone unturned" in Britain's efforts to free her. 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.
Zaghari-Ratcliffe is not the only dual national being held in Iran, but has become the most high profile case.