Iraq executed 42 "terrorism" convicts over the past week, the justice ministry said on Thursday, defying international condemnation of its extensive use of the death penalty, as deadly violence intensifies.

"The justice ministry carried out, during the past week of this month, death sentences for 42 convicts, among them one woman, all of them convicted of terrorism crimes," the ministry said in a statement on its website.

The statement, which was issued on the World Day Against the Death Penalty, was accompanied by a photo of a noose on a black background, a reference to the way in which executions in Iraq are usually carried out.

The ministry did not specify the exact dates of the executions, but the United Nations Assistance Mission for Iraq (UNAMI) said they took place between October 8 and 9.

"UNAMI reiterates its call on the government of Iraq to adopt a moratorium on the implementation of all death sentences," it said.

The latest executions bring the number of people who have been put to death in Iraq this year to at least 132, compared to 129 executions in all of 2012, according to an AFP tally based on reports from the justice ministry and officials.

Iraq executed 23 people in two days last month, 20 of them convicted on terrorism charges, the justice ministry said on October 1.

The growing resort to the death penalty comes as violence in Iraq has reached a level not seen since 2008, when the country was just emerging from a brutal sectarian conflict.

More than 250 people have been killed in violence so far this month, and more than 4,950 since the beginning of the year, according to AFP figures based on security and medical sources.

The executions have drawn widespread condemnation from the European Union, the United Nations and human rights groups.

Amnesty International issued a statement on Thursday sharply criticising the executions, noting that Iraq "is one of the most prolific executioners worldwide, after China and Iran."

"Death sentences continue to be imposed after grossly unfair trials. 'Confessions' obtained under torture on which convictions are based make it very likely that innocent people have been put to death in Iraq," said Hassiba Hadj Sahraoui, Amnesty's deputy Middle East and North Africa director.

UN human rights chief Navi Pillay said this year that Iraq's criminal justice system was "not functioning adequately."

She highlighted "numerous convictions based on confessions obtained under torture and ill-treatment, a weak judiciary and trial proceedings that fall short of international standards."

"The application of the death penalty in these circumstances is unconscionable, as any miscarriage of justice as a result of capital punishment cannot be undone," Pillay said.

But Justice Minister Hassan al-Shammari insisted on Thursday that the executions were carried out only after an exhaustive legal process.

The death sentences "were appealed more than one time before appeals court judges to prove the accuracy of the sentences," Shammari said in the ministry's statement.

Those executed were found guilty of involvement in "terrorism crimes" that "led to the martyrdom of dozens of innocent citizens, in addition to the commission of other crimes that aim to destabilise the security and stability of the country, and cause chaos and terror," the minister said.