AP | AMIR VAHDAT: British Foreign Secretary Boris Johnson arrived in Tehran on Saturday, where he is expected to discuss the fate of detained dual nationals, including a woman serving a five-year prison sentence for allegedly plotting to overthrow Iran�s government.

The British Foreign Office said Johnson would meet with Iranian Foreign Minister Mohammad Javad Zarif on Saturday to discuss �a number of consular cases involving dual nationals.� Johnson added that he would �press for their release where there are humanitarian grounds to do so.�

�While our relationship with Iran has improved significantly since 2011, it is not straightforward and on many issues we will not agree,� Johnson said in a statement. �But I am clear that dialogue is the key to managing our differences and, where possible, making progress on issues that really matter, even under difficult conditions.�

Johnson met first with Zarif. The state-run IRNA news agency said he would meet Iranian President Hassan Rouhani and other top officials during his visit.

Johnson is in Tehran as part of a three-nation Gulf tour, which the Foreign Office said was focused on the Iran nuclear deal and �how to bring an end to the conflict in Yemen.�

Iran supports Yemen�s Houthi rebels, who are at war with a Saudi-led coalition, but it denies arming them. That�s despite both Saudi Arabia and the U.S. accusing Iran of supplying the Houthis with ballistic missiles, including one the rebels used to target Riyadh on Nov. 4.

Efforts to free Nazanin Zaghari-Ratcliffe, a charity worker who has been held since April 2016, are believed to top Johnson�s agenda. Johnson recently complicated those efforts by saying incorrectly that she was training journalists when arrested. He has since apologized.

Zaghari-Ratcliffe�s husband says she faces trial on new charges Sunday that carry the possibility of an additional 16-years imprisonment, but Iranian judiciary spokesman Gholamhosein Mohseni Ejehi said last month that her verdict has been finalized.

Just ahead of Johnson�s visit, Iran�s state-run English broadcaster PressTV re-aired a documentary accusing Zaghari-Ratcliffe of planning the �soft toppling� of Iran�s government. Her family has denied the allegations.

London is considering paying Tehran some 400 million pounds from a pre-1979 arms deal. Both sides say the money isn�t related to Zaghari-Ratcliffe, though the United States made a similar payment as Iran released four U.S. citizens in 2016.

The BBC has meanwhile asked Johnson to bring up the freezing of assets of more than 150 people associated with its Persian service, something the broadcaster complained about to the U.N. in October. The BBC�s Farsi-language service was barred from operating in Iran after its disputed 2009 presidential election, though the broadcaster says the service reaches some 18 million people weekly.

Relations between Britain and Iran remain tense despite London reopening its embassy in Tehran in 2015 after a four-year closure sparked by protesters raiding it amid tensions over the country�s disputed nuclear program. Iran�s government harbors deep suspicions about both Britain and the United States, linked in part to their role in a 1953 coup that overthrew the country�s elected prime minister.

State TV and hard-liners often refer to Britain as the �old fox.� A billboard put up in Tehran before Iran�s 2016 parliamentary election showed the face of Britain�s Queen Elizabeth II replaced with that of a camel, warning voters about �foreign meddling.�

Johnson, who was in Oman on Friday, will end his trip visiting Abu Dhabi, the capital of the United Arab Emirates.

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Associated Press writer Jon Gambrell in Dubai, United Arab Emirates, contributed to this report.