Iraq executed 42 people, including a woman, for mass killings and other "terrorism" offences over the past week, the justice ministry and the UN said on Thursday after a surge in sectarian violence.

The UN mission in Iraq said it was concerned about the executions, which took place on Tuesday and Wednesday, and Amnesty International described the news as "extremely alarming".

Both urged Baghdad to immediately suspend the death penalty, which rights groups say has been used with increasing frequency by Iraqi authorities in recent years.

Sixty-eight death sentences were carried out in 2011, according to Amnesty.

The 42 hanged this week amounted to almost a third of the total number the campaign group said were put to death in all of 2012, when Iraq ranked third in a list of countries that carried out the most executions, behind China and Iran.

"The criminals were found guilty of terrorist crimes... (that) led to the deaths of dozens of innocent citizens, as well as other crimes aimed at destabilizing the security and stability of the country and causing chaos and terror among the people," Minister of Justice Hassan al-Shimary said in a statement.

More than 6,000 people have been killed in attacks across Iraq so far this year, as a Sunni Islamist insurgency that includes attacks by Al Qaeda gains momentum. - Reuters