The Government is doubling aid to flood-hit Pakistan amid mounting criticism of the international community's response to the disaster.
International Development Secretary Andrew Mitchell said the UK was offering an extra £33 million on top of the £31.3 million already pledged to help cope with the crisis.
During an emergency meeting of the United Nations' General Assembly on Thursday night to boost the foreign aid commitment, secretary general Ban Ki-moon said the floods were like "a slow-motion tsunami" that presented an ongoing crisis.
The UN said it has raised nearly half the £295m wanted for initial relief but the response remains slow.
Pakistani officials say 20 million people have been affected by the disaster, with tens of thousands of villages under water.
Speaking in New York, Mr Mitchell told the UN General Assembly it was "unacceptable" that the international community had not done more and urged other donors to step up their efforts.