The UN has said that aid for Pakistan's flood victims will focus on the survival needs of 6m people.
Médecins Sans Frontières gallery of Pakistan flooding
The agency is preparing to ramp up the relief effort with an international appeal for funds following Pakistan's worst flooding in 80 years.
The two-week crisis has seen swathes of the country cut off and raised fears of a food crisis.
'We are focusing for now on six million people who are in need of direct humanitarian assistance, meaning that they need it to survive,' said Elisabeth Byrs, a spokeswoman for the UN's Office for the Coordination of Humanitarian Affairs.
Ms Byrs said the figure of 14m affected was a broader measure given by Pakistani authorities that included the direct and indirect impact of the floods, extending from the homeless to longer term damage such as crop losses or loss of earnings.
The number of victims targeted by the appeal has yet to be finalised, but it is likely to be among one of the biggest relief efforts in the UN's history in terms of the number of people in need.
UN Under-Secretary-General for Humanitarian Affairs John Holmes will launch the international appeal for funds in New York tomorrow, along with Pakistani officials.
OCHA officials have said the disaster eclipsed the scale of the devastating 2004 Indian Ocean tsunami, the 2005 earthquake in Pakistan and the January 2010 earthquake in Haiti put together.
Ms Byrs said about 5m people were targeted by aid in the Indian Ocean tsunami, while the estimated 280,000 homes destroyed in Pakistan rivalled the numbers seen in Haiti's devastating quake.
Meanwhile, President Asif Ali Zardari has returned to the country's worst humanitarian disaster after a heavily criticised European tour.
Mr Zardari went to France on 1 August and continued on to Britain, courting massive criticism for not returning to deal with devastating floods that have left an estimated 1,600 people dead.
'The president returned home Monday night after official visits to France, Britain and Syria,' a senior government official said.
Critics, including his estranged niece Fatima Bhutto, say he miscalculated and should have cut short his visit as the crisis unfolded.
Ms Bhutto has compared the president's absence from Pakistan with the sluggish response by then US president George W Bush when Hurricane Katrina submerged New Orleans in 2005.
After his official schedule in France, Mr Zardari also made a brief private visit to Normandy in northern France, where his family owns a chateau.
