Jan. 2 (Bloomberg) -- Japanese Prime Minister Junichiro Koizumi pledged $500 million to international tsunami relief and reconstruction work, becoming the biggest donor nation.

The United Nations has mounted its biggest-ever relief operation in response to the world's worst natural disaster in 30 years. Forty-four countries have pledged $2 billion, according to Jan Egeland, United Nations emergency relief coordinator in New York.

Japan's donation exceeds the $350 million promised by the U.S., $96 million pledged by Britain and $60 million put forth by China. Taiwan announced today it's doubling its donation 10- fold to $50 million.

Koizumi and Australian Prime Minister John Howard were among the first world leaders to accept an invitation from Indonesian President Susilo Bambang Yudhoyono to attend a Jan. 6 summit in Jakarta to discuss coordinating aid and the setting up of a tsunami early warning system for the Indian Ocean.

About 150,000 people from Indonesia to the east coast of Africa died after a magnitude-9 earthquake off Indonesia seven days ago triggered tsunamis across the Indian Ocean. Indonesia was the worst-affected country, with more than 80,000 deaths.

Aid agencies estimate there are at least 5 million survivors in need of food, clean water, medical attention and funds to rebuild homes and towns leveled by the giant waves.

Japan has sent relief workers to affected areas and will consider additional dispatches of Japan Self-Defense Force members, planes and ships, the prime minister said.

``Noting the serious damage to social infrastructure in disaster-stricken countries, Japan will extend its maximum assistance possible for rehabilitation and reconstruction,'' Koizumi said in the statement.

The delivery of emergency supplies to tsunami victims has been hindered by monsoon rains that have washed out roads in Aceh province in Indonesia, the area closest to the epicenter.

Two helicopters and 29 people from the Japan's Fire and Disaster Management Agency and All Nippon Airways arrived today in the southern Thailand resort island of Phuket to begin search operations, an official of the agency said. About half the 5,000 people who died in Thailand were overseas tourists.

The number of Japanese confirmed dead in Thailand and Sri Lanka rose to 20, Japan's Ministry of Foreign Affairs overseas safety division said.

To contact the reporters on this story: Takahiko Hyuga in Tokyo at thyuga@bloomberg.net.

Last Updated: January 2, 2005 03:56 EST