UNITED NATIONS, Jan 6: With aid pledges for the devastating Indian Ocean tsunami already nearing $4 billion, the United Nations health agency warned that 150,000 people were at 'extreme risk' of dying from preventable diseases unless clean drinking water and other basic needs were restored within days.

"It goes down in the history books as the most effective assistance and relief effort ever," Emergency Relief Coordinator Jan Egeland said at a press conference here. He said that pledges of between $3 billion and $4 billion in emergency relief aid, including fresh pledges by Germany and Australia, were 'phenomenal'.

Germany announced $668 million grant which was immediately matched by the Australian government which pledged 1 billion Australian dollars which roughly translates into US $750 million.

However, UN officials pointed out that some of the money was in the form of loans or earmarked for reconstruction over three to five years rather than allocated to immediate needs.

Countries like the United States may deduct from their total pledges the costly military deployments, helicopters or ships they have put into use. The UN officials believed at least $1 billion of the pledges needed to be assigned to a country or a project.

"No one writes a blank cheque," said one official from the UN Office of the Coordination of Humanitarian Affairs, known as OCHA, which drew up the plan. The money for the projects would be allocated to 40 UN agencies or their partner non-governmental relief groups, who would supervise or carry out the tasks.

The appeal, spelled out in a 95-page report, is mainly for Indonesia ($371 million), Maldives ($66.6 million), Seychelles ($8.9 million), and Sri Lanka ($167 million). The remainder is to be spread throughout the region.