The United Nations accused Iraq on Wednesday of withholding sensitive civilian casualty figures because it fears they would be used to paint a "very grim" picture of a worsening humanitarian crisis.
Violence continued as a suicide attacker walked into a police station in volatile Diyala province and detonated a bomb, killing nine and wounding 16, police said.
Iraq's military also said it was altering a US plan to enclose a Sunni enclave in Baghdad with high concrete walls, after criticism that it would fan sectarian tension. Some residents had likened the project to Israel's West Bank barrier.
The United Nations Assistance Mission in Iraq (UNAMI) said Prime Minister Nuri al-Maliki's government would not release data on civilian deaths amid spiralling sectarian violence between majority Shias and once dominant Sunni Arabs.
"UNAMI emphasises again the utmost need for the Iraqi government to operate in a transparent manner," the mission said in its latest report on human rights in Iraq.
UN officials said they were given no official reason why their requests for specific official data had been turned down. Only broad percentages were available.
"We were told that the government was becoming increasingly concerned about the figures being used to portray the situation as very grim," United Nations Assistance Mission in Iraq (UNAMI) human rights officer Ivana Vuco told a news conference.
Maliki, whose administration has previously accused UNAMI of exaggerating civilian deaths, rejected the report as unbalanced. "The Iraqi government announces its deep reservation on the report, which lacks accuracy in the information presented, lacks credibility in many of its points and lacks balance in its presentation of the human rights situation in Iraq," a statement from his office said.
In January, UNAMI said 34,452 Iraqi civilians were killed and more than 36,000 wounded in 2006, figures that were much higher than any statistics issued by the government.
On Wednesday it said Iraq faced "immense security challenges" and a "rapidly worsening humanitarian crisis". The UN report expressed concern at the treatment of thousands of suspects detained under a major security crackdown in Baghdad, and about reports of collusion between Iraqi forces and some militias.
It also said academics, journalists, doctors and members of religious and ethnic minorities were increasingly being killed, intimidated or kidnapped by armed groups.
Iraqi officials say the civilian casualty toll has declined in the capital since the launch of the Baghdad security plan nine weeks ago. US military commanders say a surge in car bombings, however, has pushed up the overall toll countrywide.
Under the crackdown, US and Iraqi troops are sweeping through Baghdad neighbourhoods, setting up checkpoints and combat outposts and walling off some flashpoint areas with concrete barriers.
But work began to alter a 5-km (3.5 mile) concrete wall around the Sunni enclave of Adhamiya after Maliki ordered a halt to construction at the weekend following sharp public outcry.
"We have sought other substitutes such as barbed wire, sand walls and small concrete barriers," said Brigadier-General Qassim Moussawi, Iraqi military spokesman for the US-backed security plan in the city.
Both Bush and Maliki are under pressure to show progress in the crackdown after four years of war that has killed tens of thousands of Iraqis and more than 3,300 US troops. The US Congress will vote this week on a funding bill that sets March 31, 2008, as a goal for pulling out most troops but Bush has repeatedly threatened to use his presidential veto.