The UN said it has now raised more than half of its $460m aid target, although that includes pledges that have yet to be delivered.

Millions homeless

International aid group Oxfam, which had complained that European countries were "not doing enough", said it hoped the new aid would serve as a "rallying call for those EU countries that have failed to adequately respond to this disaster of an unprecedented scale".

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The news came as the UN stated that the number of people left homeless by the floods has reached four million.

Al Jazeera's Imran Khan, reporting from Sukkur in Sindh province, said: "I visited some of the more submerged, cut off, isolated villages. They were very difficult to get to.

"And when we got there they were simply ghost villages. People had just fled.

"Malaria is a huge problem in these areas because of the amount of water."

Weather experts have predicted that monsoon rains could ease over coming days, allowing aid operations in stricken region to be expanded.

The improved weather forecast comes after three weeks of torrential rains that caused devastating floods across vast swathes of the country, killing at least 1,400 people and making millions homeless.

The Pakistani government has been criticised survivors for responding slowly to the disaster. Many say they have received no help three weeks after losing everything they owned.

Anger mounting

Yousuf Raza Gilani, the Pakistani prime minister, travelled to the badly hit Swat Valley on Wednesday to meet with victims. He told Al Jazeera that he would support the victims of the disaster.

pakistan floods
At least 1,500 people killed 20 million people affected 6 million people estimated to need food aid 722,000 homes damaged or destroyed 700,000 hectares (1.7 million acres) inundated $459m needed to deal with immediate problems

"I wanted to give a message of solidarity with the people of Swat, and I promise them that the federal government, the provincial government and the people of Pakistan are with them," he said.

Bad weather, lack of funds and poor local information have combined to create "a perfect storm" of problems for the aid effort, humanitarian workers have said.

Ted Itani, from the International Red Cross and Red Crescent, operating in Pakistan, told Al Jazeera that the organisation cannot deal with the fallout from the flooding, let alone a pending second disaster caused by the outbreak of disease.

"I am hampered by [lack of] access to the beneficiaries I am mandated to serve, as well as information. We need more timely and accurate information," Itani said.

"And, thirdly, there are financial constraints because in our case I can only spend cash that is in my budget. Although donors have pledged millions of dollars it has to filter down into my account so I can order things before the onset of winter."  

Al Jazeera's Jonah Hull, reporting from Karachi, said that anger was growing at the slow response to the disaster. 

"The aid effort, both Pakistani and international, continues at a slow pace. Anger is mounting amongst survivors, many of whom have yet to receive any aid at all," he said.