LONDON (AP) — British Prime Minister Boris Johnson said Wednesday that talks were “moving forward’’ for the release of Nazanin Zaghari-Ratcliffe, who has been detained in Iran for almost six years.

Johnson confirmed a negotiating team was at work in Tehran to free Zaghari-Ratcliffe, who holds dual U.K.-Iranian citizenship. Johnson's comments were made on a visit to the Middle East, coming a day after Iran returned the passport of the charity worker.

“I really don’t think I should say much more, I’m sorry, although things are moving forward,” he told broadcasters at the Emirates Palace hotel in Abu Dhabi, United Arab Emirates. “I shouldn’t really say much more right now just because those negotiations continue to be underway.’’

Zaghari-Ratcliffe served five years in prison after being taken into custody at Tehran’s airport in April 2016. She was later convicted of plotting the overthrow of Iran’s government, a charge that she, her supporters and rights groups deny.

She has been held under house arrest and unable to leave the country since her release.