The United Nations is pegging the civilian death toll in Iraq at 34,452 in 2006 -- a sharp increase from the 12,357 reported by the Iraqi government.

Gianni Magazzeni, the chief of the UN Assistance Mission for Iraq (UNAMI), says another 36,685 were wounded in 2006.

Magazzeni told a news conference Tuesday that the wide gap between the two death tolls is because the UN figures are compiled based on information obtained through the Iraqi Health Ministry, hospitals across Iraq and the Medico-Legal Institute in Baghdad.

"Without significant progress in the rule of law, sectarian violence will continue indefinitely and eventually spiral out of control," he warned.

The Iraqi Health Ministry was unavailable for comment but the government has called previous UN statistics "inaccurate and exaggerated."

In November and December, 6,376 civilians were killed violently, mostly by gunshot wound. Most of the victims, 4,731, occurred in Baghdad, said Magazzeni.

Although high, the death toll shows a slight decrease from the previous two-month period, during which UNAMI recorded 7,047 civilians killed.

The latest bimonthly report also states that some figures were not included in December's total.

The new figures come as Baghdad prepares for a major security operation headed by Iraqi government and U.S. forces. The troops are seeking to curb sectarian violence on the rise since the bombing of a Shiite mosque in Samarra last February.

Shiite militias, specifically the Mahdi Army loyal to radical cleric Muqtada al-Sadr, have been behind much of the violence.

"The root causes of the sectarian violence lie in revenge killings and lack of accountability for past crimes as well as in the growing sense of impunity for ongoing human rights violations," the agency said.

The report also showed that 30,842 people were detained in the country in 2006, of which 14,534 were held in detention facilities run by U.S.-led multinational forces.

With files from The Associated Press