Two of those executed on Wednesday were identified as Hassan, who stabbed another man to death in 2002 and Jalal, who killed a homeowner during a robbery, the reformist Etemad Melli said.

The other two were Majid, who killed his employer over a financial dispute, and Mahdi, who was convicted of murdering a man who opposed his marrying the victim's daughter.

The hangings bring to at least 90 the number of executions in Iran so far this year, according to an AFP count.

Human rights watchdog Amnesty International reported that in 2007 Iran made more use of the death penalty than any other country apart from China, executing 317 people during the year.

The total was a sharp increase on 2006, when 177 executions were carried out, according to Amnesty International, and came amid a crackdown on criminals by police aimed at improving security in society.

Capital offences in Iran include murder, rape, armed robbery, drug trafficking and adultery.

Human rights groups have accused Iran of making excessive use of the death penalty but Tehran insists it is an effective deterrent that is carried out only after an exhaustive judicial process.