SYDNEY, May 31 (Reuters) - South Korean and Pacific Islands leaders agreed to strengthen development and security cooperation after a two-day summit where Seoul said it would double development assistance by 2027.

A joint declaration from the first Korea-Pacific Islands Summit, held in Seoul, recognised shared values of "freedom, democracy, the rule of law, human rights" and the "rules-based regional and international order".

The Pacific Islands span 40 million square km (15 million square miles) of ocean between the United States and Asia, and Western allies have moved to boost their engagement amid concerns over China's security ambitions for the strategic waters and economic leverage among the small island states.

A statement issued after the summit between South Korea's President Yoon Suk Yeol and 17 leaders and representatives from the Pacific Island Forum said "peace and stability in the Pacific region are interlinked with global peace and stability".

"The Leaders acknowledge the need to strengthen development cooperation and security collaboration including maritime security, climate security, energy security, cyber security, human security, public health and transnational security," it said.

South Korea also said it would double the scale of its development assistance to Pacific Island Countries by 2027, and supported the Pacific Islands push to preserve their maritime zones - a vital source of fishing revenue - even if climate change causes small island states to disappear beneath rising seas.

It was the third summit in a week between Pacific Island leaders and a large economy, following meetings with India and the United States.

South Korea and the Pacific Islands shared the view the ocean should be kept free of radioactive waste, and the need for international consultation and scientific assessment, the statement said, a reference to concern over Japan's plan to release water from the destroyed Fukushima nuclear plant into the sea.