Pakistani troops and relief workers are racing to reach remote parts of earthquake-hit Kashmir where thousands are feared dead.
As search and relief operations are stepped up, Pakistani authorities have updated the death toll from the quake to more than 25,000 people, with some 2.5 million made homeless.
It comes amid widespread concerns among local officials and aid groups about remote mountainous areas blocked by landslides that no one has yet visited.
Some local officials fear the final death toll in Pakistan will exceed 40,000. Another 1,200 died in Indian-administered Kashmir.
The senior United Nations relief official, Jan Egeland, on a visit to Muzaffarabad, said relief workers are facing unparalleled difficulties in the Himalayan region.
He warned that time was running out for getting help to outlying villages.
Aftershocks have continued to rock the region and are expected to continue. A 5.6 magnitude tremor jolted Islamabad this morning.
Troops report denied
Meanwhile, Pakistan has denied reports that Indian soldiers crossed the border into Pakistan-administered Kashmir to help relief efforts in the wake of Saturday's quake.
The Indian military claimed a small group of soldiers had been invited by Pakistani troops to cross the heavily fortified ceasefire line running through the disputed region.
Earlier, Pakistan's President Pervez Musharraf thanked the international community for sending relief supplies to the victims.
Pledges of around €293 million ($350m) had been received from abroad so far, the general said, while appeals domestically had raised about €14m ($17m).
Speaking in a nationwide television broadcast, General Musharraf admitted there had been delays in his government's response. He apologised but said no country could be prepared for such a disaster.
Separately, the World Health Organization has warned that outbreaks of measles, malaria and other diseases are likely in regions devastated by the earthquake.
