Iran has hanged 12 people for murder and drug trafficking over the last two days, according to Iranian media reports on Thursday.

Six people were put to death for murder in Tehran's Evin prison on Wednesday morning, the Etemad newspaper said, adding two others due to be executed at the same time were spared by the families of their victims.

On Thursday, six drug traffickers were executed in prison in Qom, a Shi'ite Muslim holy city south of the capital, the Fars News Agency quoted a judiciary official as saying.

Amnesty International has listed the Islamic Republic as the world's second most prolific executioner in 2008, after China. The human rights group says at least 346 people were executed last year in the country.

Murder, adultery, rape, armed robbery, apostasy and drug trafficking are all punishable by death in Iran.

European governments and Western rights groups have criticised Iran for an increasing number of executions since authorities launched a clampdown on "immoral behaviour" in 2007.

Iran says it is implementing Islamic law and rejects accusations it is violating human rights, accusing the West of double standards and hypocrisy.

Under Iranian law, the families of murder victims can pardon the killers, sometimes in return for financial compensation.

Etemad quoted a judge as saying some of the six people put to death in Evin were convicted of killing their spouses.

The planned execution of a ninth convicted murderer, who was 16 at the time of his crime in 1992, was postponed on the order of judiciary chief Ayatollah Mahmoud Hashemi-Shahroudi.

Rights groups have criticised Iran for executing people who committed crimes when they were under the age of 18.

On June 26, hardline cleric Ahmad Khatami called on the judiciary to charge leading "rioters" who took part in last month's post-election street protests as "mohareb" or one who wages war against God. Under Iran's Islamic law, punishment for people convicted as "mohareb" is execution.

Iran's police chief, Ismail Ahmadi-Moghaddam, on Wednesday said a total of 1,032 had been detained during violent unrest following the disputed June 12 presidential election, which was won by hardline President Mahmoud Ahmadinejad.

He said most had been freed, while the rest had been "referred to the public and revolutionary courts" in Tehran.