Pakistan's reconstruction effort after fighting forced nearly two million people from their homes could cost billions of dollars, the top UN relief coordinator warned on Friday.
Under Secretary General for Humanitarian Affairs John Holmes also warned there was no immediate guarantee of security in parts of the northwest as the government prepares to return the first of the 1.9 million displaced people.
"As for rehabilitation and reconstruction, costs should be in billions of dollars for a year or so," he told a news conference in Islamabad.
In May, the United Nations launched a flash appeal for 542 million dollars in emergency assistance, of which 42 percent has been donated.
"We are not intending a new appeal but hope that donors will respond generously to the appeal launched by the UN," Holmes said.
A massive Pakistani offensive that started in late-April in the three northwestern districts of Buner, Lower Dir and Swat sparked a huge evacuation, but army commanders say almost all areas are now clear of Taliban rebels.
Most of the 1.9 million displaced, including about 500,000 who fled an offensive elsewhere in the northwest last year, are living with relatives or in communities, while others are crammed into hot and dusty refugee camps.
Families say they are desperate to return to their cool mountain homes, but have expressed concern there is still no guarantee of security.
"The security situation is not going to be 100 percent calm in these areas overnight and we must recognise that," said Holmes, who is scheduled to leave Pakistan on Saturday after a four-day visit.
"We hope that the returns (of internally displaced persons) are voluntary and conditions are right," he added.
Prime Minister Yousuf Raza Gilani on Thursday said the displaced would start to return next Monday and tasked a special support group to finalise strategy.
UN officials say about 3,700 schools in the North West Frontier Province are being occupied by people seeking shelter from the fighting -- a matter of concern because the new school term begins on September 1.