Iraq's use of the death penalty has increased despite international condemnation, with some fearing execution rates could rise further as officials seek to appear tough on security ahead of elections.

At least 169 people were put to death in 2013, by far the country's highest such figure since the 2003 US-led invasion, and one that puts it third in the world, behind just China and Iran.

Iraqi officials insist capital punishment is both sanctioned by Islam and an effective way to curb violence, despite the fact that this year's executions have had no visible impact on the worst protracted surge in bloodshed since 2008.

Diplomats and human rights groups calling for a moratorium meanwhile point to major problems with Iraq's security forces and within the criminal justice system.

"What is more disturbing than the fact of the use of the death penalty itself ... is the fact that the utter dysfunction of the criminal justice system means that there is a very high likelihood that the people who are being executed are innocent," said Erin Evers, Iraq researcher for New York-based Human Rights Watch.

"Not just trials, but the entire security system from the moment of arrest right through the trials. It's both inadequacy of investigations, in terms of lack of professionalism, lack of collection of evidence, to corruption within the security apparatus, and between the security officers and the judiciary."

Those sentenced to death are usually hanged, often in groups.

Seven people were put to death in December, bringing the overall number for 2013 to 169, according to an AFP tally.

A total of 129 people were executed in 2012.

UN human rights chief Navi Pillay has said that Iraq's justice system is "not functioning adequately".

And the US State Department said in its 2012 Human Rights Report that "credible accounts of abuse and torture during arrest and investigation, in pretrial detention, and after conviction, particularly by police and army, were common."

But Iraq's Justice Minister Hassan al-Shammari has insisted that executions are carried out only after an exhaustive legal process.

Iraq's human rights ministry has also voiced approval, arguing that carrying out the death penalty acts as a deterrent and will help promote human rights in the long term.

"The Iraqi government has a fixed and clear stance for implementation of the death penalty against those who are found guilty because it is a deterrent to criminals and terrorists who kill Iraqis every day," Human Rights Minister Mohammed al-Sudani said in remarks posted on the ministry website.

He said Iraq still faces "a big challenge in establishing principles of human rights between generations who grew up with different values, but we hope that these principles will be spread ... gradually, especially after cutting down on terrorism, which has kept the government from spreading those principles."

The rise in executions in 2013 came as Iraq grapples with its worst prolonged period of violence since it emerged from brutal sectarian fighting that peaked in 2006-2007 and left tens of thousands dead.

And with elections coming up in April and a litany of concerns facing voters, from poor services to high unemployment, politicians will likely seek to focus attention elsewhere while ministers wanting to project toughness could even up the pace of executions.

"Executions seem to be a popular way to appear strong," said Ahmed Ali, an Iraq research analyst at the Institute for the Study of War.

"If it (an increase in executions) does happen, I don't think a lot of people will be upset about it."