Johnson is expected to win the contest to replace outgoing Prime Minister Theresa May at the end of July.
The BBC's Washington correspondent Gary O'Donoghue describe the attack as "incredibly violent" in a radio interview.
Zaghari-Ratcliffe was sentenced to prison for five years in September 2016, charged with trying to overthrow the Iranian regime.
"Of all the countries to get confused with, Japan is probably the worst one."
Hunt, a member of the British Conservative Party, has been the longest-serving health secretary in U.K. history.
The U.K.'s Department of Health said it is rolling out the scheme to improve patient safety.
High court sided with health secretary Jeremy Hunt.
Junior doctors will go on five-day strikes in September, October, November and December.
Government not deterred by threat of further major strike action.
Boris Johnson and Theresa May are the favorites to replace David Cameron.
A long-running contract dispute saw a series of historic strikes by junior doctors in England.
Increasing numbers are starting to blame both sides for the long dispute.
The government has failed to reach a deal with doctors over a new contract.
Actor Stephen Mangan said new contracts imposed on junior doctors are "ridiculous."
Junior doctors are up in arms over a new contract and its impact on women.
The British Medical Association alleges government failure to "follow due process".
Dispute continues over a new deal on overtime pay