World leaders in Jakarta pledged to closely coordinate relief efforts for the victims of the Indian Ocean disaster, and backed the creation of a tsunami warning system in the region. Part of this cooperation includes a U.S.-led group of core donor countries folding its efforts into the United Nations' operations.

U.N. Secretary-General Kofi Annan told world leaders that at least $1 billion in promised aid must be spent immediately to save lives. He warned Thursday that disease will kill more people if urgent action is not taken soon.

"To protect the maximum number of lives, to restore dignity and hope, our assistance must be timely and well-coordinated," he said. "Many of the pledges have come to us in cash and in kind; we need the rest of the pledges to be converted into cash quickly."

Mr. Annan spoke at a Jakarta meeting to coordinate long-term relief areas for the 12 nations hit by last month's disaster. Nearly four billion dollars in government and U.N. aid has been pledged to help rebuild the region.

Leaders from more than two dozen countries discussed debt relief to help affected nations rebuild, and endorsed proposals to build a tsunami warning system in the Indian Ocean.

Such a system might have reduced the death toll from the December 26 earthquake and tsunami, which left more than 150,000 people dead and millions homeless. Two-thirds of those killed were in Indonesia's Aceh province.

Indonesian President Susilo Bambang Yudhoyono warned the gathering that the task of rebuilding will be a long one.

"In the mid- and long-term, we face the challenge of rehabilitating human lives and human communities," he said. "Infrastructures must be rebuilt and sources of livelihood must be re-established."

Among the leaders at the one-day summit were Chinese Premier Wen Jiabao, Japanese Prime Minister Yunichiro Koizumi and U.S. Secretary of State Colin Powell.

To increase coordination, Secretary Powell said an early effort by the United States, Australia, India and Japan to lead relief efforts would be folded into the larger U.N.-led operation. He also indicated the U.S. aid pledge of $350 million probably would grow, but did not say by how much.

Even as the summit was going on, Aceh was rocked by aftershocks from the December 26 earthquake, frightening residents and sending many near the coast racing inland.