World leaders will meet in Indonesia Thursday to discuss aid for victims of last week's earthquake and tsunami disasters. Meanwhile, Secretary of State Colin Powell has left for Asia to visit some of the stricken areas in Thailand and Indonesia before going to the Jakarta conference.

Shortly before departing Sunday, Secretary Powell told CNN's Late Edition he believes the U.S. response to the devastation in Asia was prompt and generous. "This disaster took place just seven days ago. And during the first 24 hours, I called every single foreign minister of the affected nations, and said to them, the United States wants to help, the President stands ready to help. You let our embassies know what you need," he said.

The death toll from the 9.0 earthquake and the following tsunami is expected to surpass 150,000 people, in countries surrounding the Indian Ocean.

Washington has pledged $350 million in relief aid. But Secretary Powell said the U.S. contribution surpasses the official monetary figure. "Beyond the $350 million, our Department of Defense is spending tens of millions of dollars more, as we dispatched two carrier groups, a regular big aircraft carrier groups and a Marine amphibious group, to the region. And private donations are significant," he said.

The U.S. delegation to the stricken area includes President Bush's brother, Jeb Bush, who is the governor of Florida. The southeastern state was devastated by four hurricanes this year.

A mosque remains in a village wiped out by tsunamis in Indonesia's Aceh province

Speaking on the ABC television program This Week, United Nations Secretary General Kofi Annan said he believes it will take years for some countries to recover. "It will differ from country to country, but my own sense is you probably have five to 10 years, and billions of dollars, because the devastation is enormous," he said.

The U.N. leader also will go to the international aid conference in Jakarta. Afterwards, U.N. officials say Mr. Annan will visit the hard-hit Indonesian island of Sumatra and Sri Lanka.

Meanwhile, the World Health Organization's David Nabarro told CNN caring for the injured is at the top of his agenda. "That's priority one. But then, for the whole population, as you've said, it's clean water. We've got to make sure water supplies are not polluted with feces and that sanitation is improved. Perhaps that's proving to be particularly challenging in Indonesia, and it's not easy in Sri Lanka," he said.

Dr. Nabarro said the WHO is worried about cholera and dysentery, but has no confirmed reports of either illness yet. "And malaria incidence is not yet noted on the increase, but we are very worried about Aceh, because it's the rainy season, and it's the time when malaria does start to pick up. So, at the moment, [we hope], we have not got reports of epidemics, but it would be foolish of us to assume we're through the worst. Indeed, it's during the next week that we really have to be most concerned," he said.

Dr. Nabarro said there has been an increase in the number of cases of diarrhea in stricken areas around the region. The head of the United Nations Children's Fund, Carol Bellamy, told CNN diarrhea is especially a problem for children. "Diarrhea is something we've all had if we've traveled. But in children, it can lead to dehydration and to death. And this is something that can have an enormous impact on children," she said.

The Indonesian ambassador to the United States, Boemadi Brotodiningrat, listed other priorities. "Well, apart from food and medicines, we need shelter, because there are so many buildings which are destroyed. So, all those refugees are sheltered basically in the open area and we need tents for them," he said.

The Indonesian ambassador said his country also needs international help developing better communications.