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Ban called the floods a "slow-motion tsunami" and urged millions in additional pledges. Shah Mehmood Qureshi, the Pakistani foreign minister, also pleaded with international donors for additional aid.

"We do need international assistance, we need international assistance now," he said.

Pakistani plea

Qureshi warned the UN that food shortages could spark riots in the coming days. There have already been isolated reports of displaced persons fighting with relief workers for supplies, and the floods have pushed up food prices across the country.

More than 1.7 million acres of farmland have been submerged, much of it in Punjab province, considered the "rice bowl" of Pakistan.

"This was a mega-flood. Initially there was shock, paralysis, but we are out of it now. We are getting our acts together."

Shah Mehmood Qureshi, Pakistani foreign minister

Qureshi also pledged that his government will create "transparent and accountable" mechanisms to handle the international aid.

The Pakistani government has been strongly criticised for its slow response to the floods, and Qureshi acknowledged the scepticism and criticism.

"Initially there was shock [and] paralysis, but we are out of it now," he said at the Asia Society in New York, ahead of the UN meeting. "We are getting our acts together."

The United States, already the biggest donor, said it will commit another $60m, to bring its total aid package to more than $150m.

Donor pledge

Hillary Clinton, the US secretary of state, said approximately $92m will be used to support the UN's global aid appeal.

The United Kingdom on Thursday also vowed to increase its emergency aid: Britain's contribution will be doubled, to more than $99m. But officials told the UN that funds will only be released to partners who prove "capable" of delivering medicine, food, clean water and shelter.

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Imran Khan reports on the fortitude of those left behind in flood-hit villages

"I have come to New York directly from Pakistan, where I saw the dire need for more help," Andrew Mitchells, the British development secretary, said.

"It is deeply depressing that the international community is only now waking up to the true scale of this disaster."

The doubling of British aid, Mitchell said, "should now provide water and sanitation to 500,000 people; shelter to 170,000 people; help meet the nutritional needs of 380,000 people and provide enough health services to cover a population of 2.4 million people".

Unicef, the UN children's fund, said parts of Pakistan may remain flooded even after the rain stops. The agency warned that stagnant water will increase the risk of malaria, diarrhoea and cholera.

The floods began in the northwest of the country after exceptionally heavy monsoon rains and have since swamped thousands of towns and villages in Punjab and Sindh provinces.