The head of the U.N. refugee agency said Thursday he was concerned about the fate of more than 40,000 highland quake survivors expected to flee their mountain villages as the frigid Himalayan winter arrives.

U.N. High Commissioner for Refugees Antonio Guterres urged local officials and the international aid community to urgently prepare for the arrival of thousands of people fleeing harsh conditions and said the world must ensure that villagers who choose to remain in the ruins of their homes get the help they need to survive the next few months.

"We are doing our best to ensure that everybody, even in the most remote locations, gets enough support to face the winter and to get through the winter without tragedy," he said.

Britain on Thursday announced an additional $43 million in humanitarian relief and said Prime Minister Tony Blair would chair a roundtable discussion on relief for Pakistan at his office to be attended by representatives from the United Nations, NATO, aid agencies and the private sector. The relief pledge supplements $56 million Britain has already provided.

Guterres met with Sikander Hayat Khan, the top official in Pakistani-held Kashmir, then flew over the quake zone.

"It is absolutely awful," he said, looking out from a hillside over the rubble-strewn remains of the town of Balakot, which was largely flattened by the 7.6-magnitude quake. "I have no words to describe my feelings. I don't ever remember seeing a disaster of these proportions."

Also seeing the quake zone were Hollywood stars Angelina Jolie, a goodwill ambassador for the U.N. refugee agency, and Brad Pitt. They made an unannounced visit to Balakot and flew to a remote valley aboard a helicopter that brought food, blankets and plastic sheeting, agency officials said.

The Oct. 8 quake killed more than 74,000 people and destroyed the homes of more than 3 million in northwestern Pakistan and its part of Kashmir. About 1,350 people died in Indian-held Kashmir.

Air Commodore Andrew Walton, head of NATO's relief team in Pakistan, said providing food and medicine to people in high mountain villages was "a race in all senses of the word" before winter snow sets in and cuts off communication links.

NATO troops have provided shelter to 29,000 people, and efforts are underway to get shelters for the remaining 6,000, Walton said.

Earthquake survivors wait for humanitarian aid in the Pakistani village of Duahni Sayadan. Britain has pledged another $43 million in assistance.