Sectarian violence continued to claim the lives of a large number of Iraqi civilians in Sunni Arab and Shiite neighborhoods of Iraq's capital, despite the coalition's new Baghdad security plan, the U.N. said Wednesday.

In its first human rights report since the security plan was launched on Feb. 14 — and began increasing U.S. and Iraqi troops levels in the capital — the U.N. Assistance Mission for Iraq (UNAMI) said civilian casualties in the daily violence between January and March remained high, concentrated in and around Baghdad.

UNAMI also said that for the first time since it began issuing quarterly reports on the human rights situation in Iraq, the new Jan. 1-March 31 one did not contain overall death figures from Iraq's Ministry of Health because it refused to release them.

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The U.N. agency said the reason appeared to be that after the publication of its last human rights report on Jan. 16, Prime Minister Nouri al-Maliki's office told UNAMI its mortality figures were exaggerated, "although they were in fact official figures compiled and provided by a government ministry."

"UNAMI emphasizes again the utmost need for the Iraqi government to operate in a transparent manner, and does not accept the government's suggestion that UNAMI used the (previous) mortality figures in an inappropriate fashion," the report said.

The current report cites many examples of deadly attacks by insurgents and militias across Iraq during Jan. 1-March 31, but it often relies on media accounts of such killings and does not provide overall numbers for the period.

On Feb. 14, U.S. troops began stepping up their presence in outposts and police stations in Baghdad and areas surrounding the city, as part of the security crackdown to which U.S. President George W. Bush has committed an extra 30,000 troops. Thousands of Iraqi soldiers also are being deployed in the streets of the capital in an attempt to pacify it.

"While government officials claimed an initial drop in the number of killings in the latter half of February following the launch of the Baghdad security plan, the number of reported casualties rose again in March," the UNAMI study said.

Despite the government's announced decrease, the number of victims remained high, with up to 25 bodies still being found on some days during this period in Baghdad, the report said.

On March 1, it said, Iraq's Ministry of Interior announced that 1,646 civilians were killed in Iraq in February, most of them in Baghdad, but that "it is unclear on what basis these figures were compiled."

UNAMI said that even though its current report's evidence cannot be numerically substantiated with government figures, it shows continued high levels of violence throughout the period, including large scale indiscriminate killings and assassinations by insurgents, militias and other armed groups.

"In February and March, sectarian violence claimed the lives of large numbers of civilians, including women and children, in both Shia and Sunni neighborhoods of Baghdad," the report said.

Complete coverage is available in FOXNews.com's Iraq Center.