BAGHDAD, Iraq (CNN) -- The U.S. ambassador to Iraq warned Wednesday that "Iraq faces an urgent crisis in securing its capital."
In a Wall Street Journal op-ed column titled "The Battle of Baghdad," Zalmay Khalilzad wrote that Iraq's security depended on stopping sectarian violence in Baghdad.
"The Battle of Baghdad will determine the future of Iraq, which will itself go a long way to determining the future of the world's most vital region," he wrote. "Although much difficult work still remains to be done, it is imperative that we give the Iraqis the time and material support necessary to see this plan through and to win the Battle of Baghdad."
Khalilzad stressed the importance of the capital, saying it represents the "microcosm" of the nation, home to one-fifth of Iraq's population, and the country's "financial and media center."
"Violence in Baghdad has a disproportionate psychological and strategic effect," he said.
Khalilzad wrote the column six months after the February 22 attack on the Shiite Askariya Mosque in Samarra ignited ruthless Sunni-Shiite violence that spilled into the diversely populated capital.
He blamed the deterioration of security in the capital since those attacks on "competition between Sunni and Shiite extremists to expand their control and influence throughout the capital."
"This cycle of retaliatory violence is compounded by shortcomings in the training and leadership of Iraq's National Police," he said.
Although progress has been reported, with successes like the killing of al Qaeda in Iraq leader Abu Musab al-Zarqawi and the handover of Muthanna province to Iraqi forces, violence has increased, he said.
Last month, 558 violent incidents were recorded in Baghdad, "a 10 percent increase over the already high monthly average," he said. "These attacks caused 2,100 deaths, again an increase over the four-month average," he added.
Sectarian violence was the cause behind 77 percent of the casualties, "giving rise to fears of an impending Civil War in Iraq," Khalilzad said.
"It is clear that the people of Baghdad are being subjected to unacceptable levels of fear and violence," he said.
Economic support funds totaling $500 million from Iraq's government and $130 million from the United States will aid the effort to stabilize the capital, he said.
The Iraqi unity government's plan to secure peace in Baghdad calls for job creation and training, an expansion of local government and "improved services, such as medical care and trash and debris removal," Khalilzad said.
For the longer term, the plan will implement a program to demobilize unauthorized armed groups and review the de-Baathification process, by referring those accused of crimes to the judiciary while reconciling with the rest, he said.
Khalilzad cites a poll from the International Republican Institute, a nonpartisan group, that shows public opinion favors ethnic and religious reconciliation, despite the fighting.