UK's Boris Johnson in Iran to push for British aid workers release

UK Foreign Minister Boris Johnson landed in Iran's capital on Saturday, as he makes a direct plea to Tehran to release an imprisoned British-Iranian mother.

His visit comes after decades of troubled relations between the UK and the Islamic Republic, with Johnson only the third British foreign minister to visit Tehran in 14 years.

It follows warming relations between the two countries, after Iran agreed a nuclear deal with other world powers, including the UK.

But there are still tensions over the fate of the British aid worker Nazanin Zaghari-Ratcliffe who has been jailed in Iran on what has been described as "trumped up" spying charges.

"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," Johnson said in a statement.

He had earlier promised to leave "no stone unturned" in his mission to bring Zaghari-Ratcliffe home.

Her case is complicated by the political dynamics in the country and the fact that Iran does not recognise dual national status. Zaghari-Ratcliffe is considered "Iranian" under local law.

Iran's judiciary is also part of the anti-western conservative wing of the country’s political establishment and will not likely be swayed by Johnson's visit.

However, the prospect of fresh trade deals with the UK after years of economic isolation might sweeten some factions to pressure for her release.

Zaghari-Ratcliffe was detained during a family visit to Iran in April 2016. She was arrested at the airport while travelling with her three-year-old daughter who remains in Tehran with her grandmother. 

Her husband Richard Ratcliffe remains in the UK and has met Johnson on helping securing his wife's release.

Johnson sparked immense criticism after he wrongly stated Zaghari-Ratcliffe was in Iran to teach journalism, a blunder which could have led to her sentence being extended.

Zaghari-Ratcliffe worked for the Thomas Reuters Foundation, a charity independent of the news agency, however, she was in Iran on a personal visit when she was arrested.

Johnson has already met Oman's Sultan Qaboos bin Said during a visit to Muscat.