"There is a terrible security situation there with an increasing number of people who are displaced," Nancy Aossey, the president of the International Medical Corps (IMC), told Reuters.
The California-based group said in a study published on Monday, January 29, on its website that 546,078 Iraqis had been displaced since February 2006.
It found that 80 percent of the displaced were from Baghdad, adding that sectarian violence has driven 181,000 Baghdadis from their homes in the last three months alone.
The American group, which has more than 300 staff in Iraq, warned that the exodus was rising at a "dramatic rate," particularly in the capital.
"The pace of the departures is accelerating rapidly — the number of those displaced has increased by 43% since November," it said.
The organization's estimates are higher than those issued by the United Nations earlier this month.
The UN says some 1.7 million people are internally displaced and about 2 million more are sheltering outside the country, comprising a worrying 12 percent of the total population.
Almost 34,000 civilians died last year as the raging sectarian violence reached new heights, above all in Baghdad, according to the latest death count published by the government.
US President George W. Bush is planning to send an extra 21,500 troops to Baghdad over the next few weeks to crush sectarian militias in the violence-hit capital.
First results from the new deployment can be expected from mid-February, but it will not be clear until the middle of the year whether the strategy has been successful.
The American charity group said the current exodus appeared more "permanent," with people abandoning or selling their homes.
It said earlier movements that followed the 2003 US-led invasion were often forced by short-term military operations.
"The departures are reshaping the city along sectarian lines, much as Sarajevo was reshaped by ethnic fighting in Bosnia-Herzegovina in the early 1990s," it said.
"Some of the displaced have sought refuge with family or friends in 'sectarian friendly' neighborhoods within the capital, while others have fled the capital altogether to outlying governorates."
Adnan Al-Dulaimi, the leader of the Sunni National Accord Front, has accused Shiite militias of trying to change Baghdad's Sunni demography through waves of sectarian killings and forcible evacuations.
"This plot is based on killing and intimidating Sunnis, forcing them into a panicky flight from Baghdad and its suburbs to change the demography," he told IslamOnline.net in a recent interview.
The Pentagon, in a recent report, described the Shiite Mahdi Army militia as the biggest threat to security and the main culprit behind the surge in civilian deaths.
The International Medical Corps (IMC) said that the phrase "humanitarian crisis" typically describes conditions now unfolding in Iraq.
"It is a brewing humanitarian crisis of enormous proportions that is being overshadowed by the fighting itself and the debate surrounding the war," Aossey said.
The study said long-term displacement seriously reduces the ability of many Iraqis to sustain their livelihood.
It added that many of those displaced had poor access to food and irregular supplies of government rations resulting from the deteriorating security situation.
The IMC said ill-equipped health care centers could not cope with extra patients.
"There is a chronic shortage of medication, lab materials and X-ray films in the country which renders many health facilities useless."
Aossey appealed to the world to help, particularly in getting people health care and steady food supplies.
The UN High Commission for Refugees (UNHCR) said earlier this month that Iraqi refugees are living in deplorable conditions in host countries.
It said some woman refugees were forced to resort to prostitution in addition to growing child labor problems.
(Click to Read the Study