Iranian state media says that ten convicted murderers have been put to death in a single day.
On Wednesday morning, the men were hanged at a jail in the capital, Tehran, the Iran newspaper reported.
The authorities have taken to carrying out mass executions because they see it as an extra deterrent, said the BBC’s correspondent in Iran.
Iran is thought to have put to death more than 150 people last year. Rights groups say only China executes more.
The latest executions took place in Tehran, at Evin prison.
Government-owned media said the convicts included a robber who killed a taxi driver, a drug addict who killed his aunt, and another man who murdered three members of a family with whom he was having a dispute.
In Iran, murder, rape, armed robbery, drug trafficking and adultery are all punishable by death.
As the government does not publish figures on executions, estimates on the numbers of people put to death are often based on media reports.
Even though most criminals are hanged, two men were recently stoned to death for adultery.
Pictures of the convicts making their way to the gallows are sometimes shown on TV, said the BBC’s Jon Leyne, in Tehran.