UK foreign secretary in Iran to push for Briton's release

Foreign Secretary Boris Johnson will arrive in Iran early Saturday, where he will press for the release of a British-Iranian woman held in prison, according to Britain's Foreign Office.

Johnson, who will meet with his Iranian counterpart Javad Zarif, will also discuss the Iranian nuclear deal, the conflict in Yemen and other key regional issues.

In advance of his arrival in Tehran -- the first by a British foreign secretary since 2015 -- Johnson said he expected "a constructive visit".

"I will stress my grave concerns about our dual national consular cases and press for their release where there are humanitarian grounds to do so," he vowed.

Part of a three-day trip to the region, it unfolds amid mass protests across the Muslim world following US President Donald Trump's announced move of the US embassy to Jerusalem.

Johnson stopped in Oman on Friday, and will move on to the United Arab Emirates Sunday.

"Iran is a significant country in a strategically important, but volatile and unstable, region which matters to the UK's security and prosperity," Johnson added.

"While our relationship with Iran has improved significantly since 2011, it is not straightforward and on many issues we will not agree," he added.

"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."

Nazanin Zaghari-Ratcliffe, a British-Iranian citizen, was arrested at Tehran airport on April 3, 2016, after visiting relatives with her young daughter.

Iranian authorities accused her of links to mass protests in 2009, which she denies, and sentenced Zaghari-Ratcliffe to five years in jail for sedition.

Last month they filed additional charges of "spreading propaganda" and will present her in court again on Sunday.

Johnson appeared to jeopardise her defence last month by saying she was training journalists during her visit -- something her employer, the Thomson Reuters Foundation, and her family strongly deny.

The foreign secretary later clarified his remarks, saying it was clear that she was only on holiday.

Husband Richard Ratcliffe, who had lobbied to join Johnson on the visit, has raised concerns about his wife's mental health, citing the mounting toll of incarceration.