"It is no longer so hard to imagine what might happen from the rising sea levels that the world's top scientists are telling us will accompany global warming," Annan told leaders at a UN conference on small islands here.

"Who can claim that we are doing enough?" he asked.

The conference that opened on Monday is looking at ways to help the world's most vulnerable states cope with hazards and disasters such as the December 26 tsunami that devastated 12 countries, including the Maldives, a cluster of 1,192 low-lying islands scattered across the Indian Ocean.

Delegates from small islands such as the Pacific state of Tuvalu, whose very existence is threatened by rising sea levels, are pressing for action on climate change and charged that they were facing resistance from the United States and other countries.

"We must also be ready to take decisive measures to address climate change," said Annan, who arrived here after touring tsunami-hit Indonesia, Sri Lanka and the Maldives.

His remarks came a month ahead of the entry into force of the Kyoto protocol on climate change that will see 38 countries reduce their greenhouse gas emissions, seen as the main cause of global warming. The United States, one of the world's biggest polluters, has refused to endorse the protocol.

Annan called for setting up a global early warning system to avert another tragedy on the scale of the Asian tsunami that left 158,000 dead.

He said the new system should cover "not just tsunamis but all other threats, such as storm surges and cyclones."

"In such an endeavour, no part of the world should be ignored," he said.

The UN's education and scientific agency UNESCO is leading an effort to set up a global early warning system that it said should be up and running for the Indian Ocean region in June 2006, with a worldwide mechanism in place a year later.

In his address to the leaders of the world's more than 40 island-states, Annan lamented that an action plan launched in 1994 to help the small nations had failed to yield results.

International aid to small developing states has dropped from 2.3 billion dollars to 1.7 billion dollars over the past decade, UN officials say, while at the same time, the islands have been struggling with the loss of trade preferences.

"Barely above sea level, remote from world markets, many small island states occupy the margins of our global community," Annan said. "For some, their very existence is in jeopardy."

"We are all inhabitants of the global island," he said. "All of us, rich and poor, weak and strong, whether citizens of great power or tiny atoll, are linked in webs of opportunity and vulnerability."

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