The number of people driven from their homes by months of fighting in western Iraq's Anbar province may have spiralled to nearly 480,000, the UN refugee agency warned on Friday.
"As of today, the Iraqi government says 434,000 men, women and children have fled their homes since fighting escalated in January this year," said UNHCR spokesman Adrian Edwards.
"However, the full scale of the displacement from this under-reported conflict is unknown, as the Iraqi authorities have had to suspend registration over the past month because of insecurity.
"UNHCR believes the current figure is now close to 480,000," he told reporters in Geneva.
A special UNHCR appeal to help the victims of the crisis was launched in March but has only gathered 12 percent of the $26.4 million (19 million euro) needed, he said.
The crisis in Anbar, which shares a long border with civil war-hit Syria, erupted in late December when security forces dismantled a longstanding Sunni Arab protest camp near provincial capital Ramadi.
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Anti-government fighters subsequently seized the city of Fallujah, just a short drive from Baghdad, and parts of Ramadi, farther west.
Despite months of clashes, shelling and missile strikes in various areas of the province, no resolution is in sight.
Displacement jumped after fighters deliberately breached a dam in Anbar, flooding the area and forcing some 72,000 people from their homes, Edwards said.
That has compounded the crisis because people are struggling to secure access to clean water, raising health risks.
"Local officials say 28 tanker truckloads of potable water are being delivered to the area every day, but this is only meeting 50 percent of needs," said Edwards.
In addition, there are fears that more civilians will flee the city of Fallujah, where recent shelling hit a hospital and water plant, he said.
Violence is meanwhile hampering efforts to help those in desperate need.
"We urgently need to ramp up our response which is difficult for three reasons: We have deteriorating security in Anbar hindering access to people in need, the displaced are spread out across much of the country, and donor support is lacking," said Edwards.