The British-Iran national, who is currently under house arrest in Iran, has been told she must attend court on Monday and prepare to return to prison following the hearing.
The 42-year-old has been held in the country since April 2016 when she was arrested at Tehran airport following a visit to her parents to introduce them to their granddaughter.
Ms Zaghari-Ratcliffe was convicted of spying and jailed for five years, although she was released under house arrest in March this year as coronavirus swept through Iran's prisons.
Dominic Raab said on Friday morning: “The truth is the detention of Nazanin and other dual nationals in Iran is totally unwarranted, we've made it very clear we want to put the relationship between the UK and Iran on a better footing.
“If Nazanin is returned to prison that will of course put our discussions and the basis of those discussions in a totally different place.
“It is entirely unacceptable, it is entirely unwarranted, it is totally unjustified.”
Speaking to Radio 4's Today Programme, Mr Raab said: “I totally understand the horrific position she is in.”
He said it has been made clear to Iran that any move to bring fresh proceedings against Ms Zaghari-Ratcliffe “must not happen” .
On Thursday evening, Iranian ambassador Hamid Baeidinejad was summoned to a meeting at the Foreign Office (FCO) where he was told of the UK's “grave concern” at the development.
FCO director-general for the Middle East Thomas Drew said the ambassador was told the move was “unjustified and unacceptable, and is causing an enormous amount of distress”, a spokesman said.
Ms Zaghari-Ratcliffe has been afforded diplomatic protection by the UK government, which states she is innocent and her treatment by Iran failed to meet obligations under international law.
She and her family believe she is being held as political leverage to try and force the UK's hand in a long-running financial dispute between the two countries.
It dates back to the 1970s when the then-Shah of Iran paid the UK £400m for 1,500 chieftain tanks.
When he was toppled in 1979, Britain refused to deliver the tanks to the new Islamic Republic but kept the cash, despite British courts accepting the money should be repaid.
The Iranian authorities have denied any link between the debt and Ms Zaghari-Ratcliffe's imprisonment.
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