Britain on Friday extended the status to Nazanin Zaghari-Ratcliffe, who was arrested in Tehran in 2016.
"If it does not make the situation more complicated, it will surely not make things easier."
Zaghari-Ratcliffe, who worked for the Thomson Reuters Foundation -- the media organisation's philanthropic arm -- is serving a five-year jail sentence for sedition.
She has denied all the charges against her.
Diplomatic protection is a rarely-used mechanism allowing governments to seek protection for their citizens on the grounds that they have been wronged by another state.
This would signify the "formal recognition by the British government that her treatment fails to meet Iran's obligations under international law", he said.
But Ghasemi denied this, saying Zaghari-Ratcliffe is "enjoying all legal and citizenship rights -- both throughout her trial proceedings and during the conviction period", including medical care.
Ghasemi dismissed the move as "merely reflecting a political decision by the UK" and said that it would not "in itself bring about a new legal status internally or internationally."
Iran's envoy to London said last week that the UK's decision "contravenes international law", as governments can only exercise such protection for their own nationals.
"Irrespective of UK residency, MS Zaghari thus remains Iranian," he wrote.
(This story has not been edited by Business Standard staff and is auto-generated from a syndicated feed.)