Islamabad, Pakistan ? Tent camps sheltering earthquake victims in devastated northern Pakistan may be needed for another six months, a U.N. official said Saturday, as the United States signed a $200 million grant for rebuilding the country.

Visiting U.S. Undersecretary of State Nicholas Burns signed over the aid money, part of $510 million earlier pledged by Washington, the U.S. Embassy in Islamabad said. The grant covers four years, with the first $15 million available Saturday.

Burns said the money would go toward rebuilding schools and hospitals destroyed when the massive Oct. 8 quake struck Pakistan’s Kashmir region and surrounding areas.

The aid came after a U.N. report said the harsh Himalayan winter was testing the population’s strength and resilience and “the capacity of the humanitarian community to deliver much-needed relief.”

By summer, some people whose homes were reduced to rubble, washed away in floods or buried in landslides will still need temporary shelter, said Ben Malor, a spokesman for the U.N. Office for the Coordination of Humanitarian Affairs.

“We want to believe at this point that the number will be small,” he said Saturday.

His agency’s report, released Friday, said safe drinking water was available to only about 47 percent of 810,000 refugees initially targeted for the winter. Access to latrines is available to only about 138,000 – about half the winter target.

The assessment highlights the misery felt by nearly 3.5 million people left without their homes in freezing conditions by the magnitude 7.6 earthquake.

Heavy snow and rain have forced repeated suspensions of aid flights, while landslides have cut off deliveries by trucks.

The earthquake killed 87,000 people, but aid workers worry the death toll will rise as winter weather intensifies hunger and misery.

Many are without adequate shelter, clothing and are heavily reliant on food aid.