Japan has promised to give aid to five Mekong nations, whose leaders are in Japan for high-level talks aimed at fostering development and friendship. The resource-rich region is also being courted by China.
Leaders of Cambodia, Laos, Myanmar, Thailand and Vietnam met on Saturday, with host country Japan promising $7.4 billion (5.6 billion euros) in aid to the region.
The morning summit was the fourth of its kind and provided an important diplomatic platform for Myanmar as it regains credibility in the international community.
"The stability and prosperity of East Asia will not be possible without the stability and prosperity of the Mekong region," Prime Minister Yoshihiko Noda told a joint press conference.
"The Japanese government will recognize the Mekong region as a significant destination of assistance and continue its cooperation strongly," said Noda at the end of the six-way summit.
Thai Prime Minister Yingluck Shinawatra, Vietnamese Prime Minister Nguyen Tan Dung, Laotian Prime Minister Thongsing Thammavong and Cambodian Prime Minister Hun Sen gave a commitment their nations would use the Japanese aid efficiently.
Competition for influence
Beijing and Tokyo have for years vied for influence in the Mekong Delta region, situated around the lower stretches of the 4,800-kilometre (2,980-mile) Mekong River.
Japan maintained trade and dialogue with Myanmar throughout its years of isolation, warning the West that to alienate the repressive military junta could force it closer to China.
The five countries have historically been isolated by war and political turmoil. With the region poorer than most other parts of Southeast Asia, it is seen as an important potential source of cheap labor for export-driven Japan.
Prime Minister Yoshihiko Noda had also been expected to meet Myanmar President Thein Sein separately, being expected to forgive $3.7 billion in debt and begin a suspended assistance program to the country.
rc/sb (AFP, dpa)