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

"I am appalled by the execution of British-Iranian citizen Alireza Akbari in Iran," 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." (Reporting by Michael Holden, Editing by Angus MacSwan)