British Foreign Secretary Boris Johnson met Iranian President Hassan Rouhani for nearly an hour on Sunday in his attempt to secure the release of British-Iranian Nazanin Zaghari Ratcliffe.
The two men "spoke forthrightly" and "agreed on the need to make progress in all areas," the British Foreign Office said afterwards.
But the fate of Zaghari-Ratcliffe, who was sentenced to five years in prison in January on charges of espionage and sedition, remained unclear with neither side saying if progress was made in the case.
Johnson arrived in Tehran on Saturday and held "frank" talks with his Iranian counterpart Mohammad Javad Zarif about the jailed Briton during a two-hour meeting which also dealt with other issues. 
A gaffe by Johnson in the British parliament last month led Iranian authorities to claim he had confirmed that Zaghari-Ratcliffe - who was on holiday in Iran to introduce her baby daughter to her parents - had trained journalists while in the country.
The dual British-Iranian citizen had been working in London as a project manager for the Thomson Reuters Foundation. Iran does not recognise dual nationality.
The Iranian ambassador to Britain, Hamid Baeidinejad, on Saturday dampened hopes of a quick release for Zaghari-Ratcliffe, saying her case was in the hands of the Iranian judiciary, not the government.
However, a hearing scheduled for Sunday at which Zaghari-Ratcliffe was expected to appear was postponed, according to her husband, Richard Ratcliffe. 
"Nazanin's court case was not held today in the wake of the foreign secretary's visit," Ratcliffe said, as reported by the Press Association. "This is undoubtedly a good sign." 
"The foreign secretary also met with Nazanin's family last night to reassure them that Nazanin was a close concern, and that her case had been discussed in every meeting he held," said Ratcliffe.
"I am expecting a fuller debrief from the Foreign Office on the foreign secretary's efforts on Nazanin's case once he returns from the region, either Monday or Tuesday."
There have been suggestions in London and Tehran that if Britain paid back a historical debt of £450mn ($600mn) it could help the case of Zaghari-Ratcliffe and a small number of other
dual nationals being held in Iran.
Baeidinejad, however, rejected reports in British media that the decades-old debt payment was being used as a ransom tactic.
The debt dates back to the 1970s when Iran paid Britain for 1,500 army tanks. Only 150 were ever delivered because Britain refused to complete the order after Shah Mohammad Reza Pahlavi was overthrown in 1979. 
Johnson's trip is the first by a British foreign secretary to Iran since 2015 and only the third since 2003.
During the two-day trip he also met Vice President Ali Akbar Salehi, who oversees Iran's nuclear activities. Johnson had said he would press Iran to stick to the terms of the landmark 2015 deal that curtailed Tehran's nuclear programme.
Iranian media said Rouhani expressed frustration that despite the easing of sanctions, many major European banks, wary of falling foul of the United States, have refused to finance Iranian businesses.
Related Story