A woman and three men were hanged in the northwestern city of Zanjan, Iran after they were found guilty of drug trafficking.
The identity of the four were not disclosed but the executions were carried out in Zanjan's main prison.
The execution brings to at least 129 the number of hangings for this year in Iran. In 2009, 270 were executed.
Iran applies capital punishment only after exhaustive judicial proceedings. It says death penalty is important to maintain public security.
Adultery, armed robbery, drug trafficking, murder and rape are all punishable by death in the Islamic republic.
Similar to China, Saudi Arabia, and the United States, Iran is one of the leading countries that carry out hanging each year.