Climate change is generating an "unholy brew" of extreme weather events that threaten global security, the UN chief said Wednesday as the Security Council recognized the issue's potential effect on world peace.

But the 15-member council apparently failed to agree on whether climate change itself was a direct threat to international peace and security, even after a rebuke by the United States which described the lack of consensus as "pathetic."

Secretary General Ban Ki-moon urged concerted action and called on developed countries to lead the charge in mitigating effects of climate change, while encouraging the developing world to do its fair share.

"Extreme weather events continue to grow more frequent and intense in rich and poor countries alike, not only devastating lives, but also infrastructure, institutions, and budgets -- an unholy brew which can create dangerous security vacuums," Ban told a Security Council debate on the issue.

Climate change, he said, "not only exacerbates threats to international peace and security; it is a threat to international peace and security."

The Security Council issued a presidential statement in which it "expresses concern that possible adverse effects of climate change may, in the long run, aggravate certain existing threats to international peace and security."

But it stopped short of calling climate change a threat in itself, despite pleas to do so by Pacific small island developing states.

A statement from the French delegation expressed "disappointment" over the lack of "punch" to the UN statement.

"The face that a unanimous agreement was reached at the Security Council represents a remarkable advance," it said, but France "regretes that it was not able to reaction a consensus on a more ambitious presidential declaration."

Nauru President Marcus Stephen spoke for states such as the Maldives and Seychelles at the meeting, warning that several islands could disappear altogether, forcing large cross-border relocations.

He said that while the council members understood such security challenges, he said sympathetic words were not enough.

"Demonstrate it by formally recognizing that climate change is a threat to international peace and security," Stephen said.

Speaking before the Security Council issued its statement, US ambassador to the United Nations Susan Rice blasted the council for being unable to reach a strong consensus despite "manifest evidence" that climate change posed a direct threat to peace and security.

"This is more than disappointing. It's pathetic, it's shortsighted, and frankly it's a dereliction of duty," she said.

A US diplomat, who declined to be identified, said later the UN statement was "obviously lacking force" but called it "a small step in the right direction."

According to a UN readout of the debate, China envoy Wang Min said climate change could affect security, but it was essentially a sustainable development issue and the council did not have the resources to address it.

Russia's UN envoy Vitaly Churkin said that while his government shared the concerns of island states regarding rising sea levels, the UN's climate convention remained the fundamental way to address the problem.

He also said Moscow was skeptical about repeated attempts to place climate change on the council's agenda.

Achim Steiner, director of the UN Environment Program, cited a worst-case scenario prediction that temperatures will rise four degree Celsius by 2060 while the sea level will rise one meter (3.3 feet) over the next century.

There are myriad threats already and their numbers will rise, he said, noting droughts like the one currently afflicting Somalia, floods such as the ones that hit Pakistan, and their implications on the food markets.

"The scale of the natural disasters will increase exponentially," he added.

Two regions of southern Somalia, hit by a devastating drought, were declared to be in a state of famine Wednesday by the United Nations, which called it the worst food crisis in Africa in 20 years.

The next climate conference will take place in Durban in December.