The United Nations suspended lifesaving relief flights to quake-hit Kashmir on Sunday as heavy snow grounded helicopters and promised more misery for millions left homeless in freezing temperatures.

The flights, which form the bulk of the mammoth relief operation, may resume Monday if there is a break in the weather, U.N. spokesman Ben Malor said. "We are hoping tomorrow that things will clear up," he said Sunday.

Monday marks exactly 100 days since the giant earthquake struck, killing 87,000 people and leaving about 3.5 million homeless.

Pakistan's Meteorological Department is forecasting heavy snow to keep blanketing the quake zone over the next five days, possibly triggering avalanches along its jagged peaks.

Temperatures are expected to remain below freezing, fanning concern about a possible spike in cold-related illnesses, especially among the young and elderly.

"The relief operations will be affected badly," the Pakistan Meteorological Department said.

Most of the victims in the Oct. 8 temblor were from Pakistan's North West Frontier Province and the Pakistani-administered part of the divided Himalayan territory of Kashmir. But another 1,350 were killed in India's portion of Kashmir.

This was the second time this year the United Nations has suspended aid flights.

Bad weather grounded helicopters for three days earlier this year, delaying the shipment of nearly 1,000 tons of supplies over the period, Malor said. The United Nations flies aid to 186 different sites in the quake-affected area.

Relief workers are racing to ship as much as aid possible to the quake zone, concerned that harsh winter weather will trigger a second wave of deaths on top of the tens of thousands who have already died.

The United Nations is now focusing on more aid to the often squalid spontaneous refugee camps that have popped up in the quake zone, sites often lacking weather-resistant tents.

Officials are also preparing to receive up to 60,000 survivors who may try to escape the winter cold by evacuating mountainous regions and move to lower-lying areas.

"Our rapid assessment of needs after the first biting taste of winter suggests that we need to do more for people in these unplanned camps below the snow line," U.N. relief coordinator Jan Vandemoortele said in a statement issued Saturday.

There are currently 26 planned refugee camps being run by the Pakistan military with assistance and provisions from U.N. agencies and other donor organizations.

By contrast, there are about 118 unplanned camps.