Twenty criminals were hanged in a single day this week in western Iran, local media reported Thursday.
The men, executed on Tuesday, had killed dozens of people, including women and children, the Justice Bureau in Kurdistan said.
The bureau accused the men, described as members of a Sunni terrorist and criminal group in Kurdistan province, of attacks on police stations which had killed several officers.
Although described as terrorists by officials, the hanged men are unlikely to be members of militant political or ideological groups such as Islamic State.
The mass hanging is far from the first such incident in Iran.
The Islamic republic has the world's highest rate of hangings. According to rights group Amnesty International, 977 people were executed in the country in 2015, and 700 since the beginning of this year.
In 2008, 29 convicts were executed in one day in Tehran.
Doubts over the use of capital punishment are growing within the establishment however.
Criminal activity - in particular related to drugs smuggling - shows no sign of reducing. Regular executions are also seen to be hurting attempts by President Hassan Rowhani to present Iran as a moderate Islamic state.