Michael Gove appeared to leave doubt over the actions of a British woman jailed in Iran after saying he did not know why she was in the country.
In a staunch defence of Boris Johnson, who has been criticised for making remarks that were seized on by Tehran to justify its threats to extend the sentence of Nazanin Zaghari-Ratcliffe, Mr Gove attacked attempts to shift the blame from "who is really at fault".
The country's state TV broadcaster has claimed the Foreign Secretary's suggestion she was "training journalists" in Iran at the time of her arrest last year amounted to an "unintended admission" of her guilt.
Asked what Mrs Zaghari-Ratcliffe was doing in Iran, Mr Gove told BBC One's The Andrew Marr Show: "I don't know.
"One of the things I want to stress is there is no reason why Nazanin Zaghari-Ratcliffe should be in prison in Iran so far as any of us know."
The Environment Secretary warned it would be a "big mistake" to focus attention on his Cabinet colleague when Iran is "in the dock".
He said: "There is an effort, somehow, to shift attention and direction away from who is really at fault her and it is the Iranian regime."
There is "no reason" for Mrs Zaghari-Ratcliffe's detention and she should be released, he said.
"There is nothing the Iranian regime would like more than for the attention to be shifted off them and on to us", Mr Gove said.
"I think we make a big mistake if we think the right thing to do is to blame politicians in a democracy who are trying to do the right thing for the plight of a women who has been imprisoned by a regime that is a serial abuser of human rights.
"Who is in the dock here? Iran."
"Let's not play their game.
"We play their game if we point the finger at democrats who are trying to do the right thing when it is extremists who are responsible for the abuse of human rights.
Mr Gove said Mr Johnson was "doing a great job" as Foreign Secretary and that it was "plain wrong" to find fault with democrats when Iran is a regime that has "blood on its hands".
Told that Richard Ratcliffe said his wife was in Iran on holiday, Mr Gove added: "In that case, I take exactly her husband's assurance in that regard."
Asked if she had been training journalists, he said: "Her husband said she was there on holiday and her husband is the person who should know."
Shadow Cabinet office minister Jon Trickett said: "Boris Johnson's cavalier approach to international diplomacy is compounded this morning by Michael Gove claiming he has no idea what Nazanin Zaghari-Ratcliffe was doing in Iran. It has always been clear, she was on holiday visiting her family.
"It appears Gove is more interested in protecting Johnson's job than the liberty of a British citizen in jail in Iran.
"Theresa May must ensure Nazanin Zaghari-Ratcliffe does not pay the price for her ministers' bungling."
Mr Johnson is understood to have had a "constructive" conversation with Mr Ratcliffe on Sunday morning by telephone.
They agreed to meet next week or the following week.