LONDON, Jan 14 (AFP) - Britain on Saturday called the execution by Iran of British-Iranian national Alireza Akbari a barbaric act and said it would not go unpunished.

Earlier, the Iranian judiciary's Mizan news agency reported the execution of the former Iranian deputy defence minister who had been sentenced to death on charges of spying for Britain.

"I am appalled by the execution of British-Iranian citizen Alireza Akbari in Iran," British Prime Minister Rishi Sunak said on Twitter. "This was a callous and cowardly act, carried out by a barbaric regime with no respect for the human rights of their own people."

British Foreign Secretary James Cleverly also tweeted to say: "This barbaric act deserves condemnation in the strongest possible terms. This will not stand unchallenged."