Einollah G., 55, Abdolrahman N., 33, and Abolhasan Sh., 38, were hanged in public on Saturday morning in Bandar Abbas, the capital of Hormozgan province, the student ISNA news agency said.
Einollah G. was found guilty of smuggling 90 kilos (198 pounds) of opium and the other two were executed for carrying four kilos (nine pounds) and five kilos (11 pounds) of heroin respectively.
Ghader Radsar was hanged in a prison in Zahedan, southeastern Sistan-Baluchestan province, on Thursday for carrying 12 kilos (26 pounds) of heroin, a report in the hardline Kayhan newspaper said.
The hangings bring to at least 46 the number of executions in Iran this year. At least 154 people were executed in 2006, according to an AFP tally based on press and witness reports.
Capital offences in the Islamic republic include murder, rape, armed robbery, apostasy, blasphemy, serious drug trafficking, repeated sodomy, adultery or prostitution, treason and espionage.