Nearly 35,000 civilians were killed last year in Iraq, the United Nations said Tuesday, a sharp increase from the numbers reported previously by the Iraqi government. Gianni Magazzeni, the chief of the UN Assistance Mission for Iraq, said 34,452 civilians were killed and 36,685 were wounded last year. Iraqi government figures in early January put last year's civilian death toll at 12,357. When asked about the difference, Magazzeni said the UN figures were compiled from information obtained through the Iraqi Health Ministry, hospitals across the country 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. Magazzeni said 6,376 civilians were killed violently in November and December - 4,731 of those in Baghdad, most as a result of gunshot wounds. He noted that was a slight decrease from the previous two month period, during which UNAMI recorded a total of 7,047 civilians killed. The mission's latest bimonthly report also noted that figures from some governates were not yet included in the total for December. The figures were released as Baghdad braces for a major security operation to be launched by the Iraqi government and US forces aimed at quelling the rampant sectarian violence that has been on the rise since the Feb. 22 bombing of a Shiite mosque in Samarra. Much of the violence has been blamed on Shiite militias, particularly the Mahdi Army militia that is loyal to radical cleric Muqtada al-Sadr, a key supporter of Prime Minister Nouri al-Maliki. Dozens of bodies turn up on the streets of Baghdad daily, many showing signs of torture. "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 on-going human rights violations," the agency said, calling on the Iraqi government to step up efforts to restore law and order. The Iraqi Health Ministry could not immediately be reached for comment, but the government has disputed previous figures released by the UN as "inaccurate and exaggerated." The UN report also said that 30,842 people were detained in the country as of Dec. 31, including 14,534 in detention facilities run by US-led multinational forces.