The husband of jailed Iranian-British aid worker Nazanin Zaghari-Ratcliffe says there have been "positive steps" toward her release following British Foreign Secretary Boris Johnson's visit to Tehran last week.

Zaghari-Ratcliffe has been held by Iranian authorities since April 2016 for allegedly plotting against Iran's government, which she denies.

Richard Ratcliffe said his wife's treatment has improved in Tehran and he remained optimistic that she would be released.

"I spoke to her yesterday and she was much more positive because the conditions were improving and just because she's hopeful that after, you know, 20 months, she can be finally be reunited with her daughter and her husband," Ratcliffe said in an interview with RFE/RL's Radio Farda on December 15.

Ratcliffe said his wife has been allowed to call him every day and she has been granted extra family visits since Johnson's visit to Iran from December 9-10.

He also said authorities had dropped fresh charges against her for "spreading propaganda."

"I've seen positive steps coming out of Iran in terms of the way she has been treated better, in terms of the way her court case has been closed, and in terms of the way there's been movement in that application for early release," he said. "No guarantees, but they're positives."

Johnson met with senior Iranian leaders as he continued efforts to gain the release of Zaghari-Ratcliffe.

Ratcliffe said he had an hour-long talk with Johnson after he landed back in London on December 11.

"He stressed that he was doing all he could do," Ratcliffe said. "He suggested that maybe too much campaigning doesn’t help. I said, ‘I think it’s important for me to be consistent, keep going, and be clear to an Iranian audience that I will keep campaigning until she’s home.’”

Ratcliffe said the "dream" to have Zaghari-Ratcliffe back home in Britain in time for Christmas was "still alive."