LONDON - British Prime Minister Gordon Brown said Wednesday that climate change and pandemic disease threaten international security as much as terrorism and that Britain must radically improve its defenses.

Brown listed the greatest threats to Britain's peace as "war, terrorism and now climate change, disease and poverty -- threats which redefine national security."

"The nature of the threats and the risks we face have -- in recent decades -- changed beyond recognition and confound all the old assumptions about national defense and international security," Brown told lawmakers in the House of Commons.

A classified list of threats to national security will be released to the public later this year, he said.

"Climate change is potentially the greatest challenge to global stability and security," a report commissioned by Brown to outline the new strategy said.

British officials estimate a flu-type pandemic in the U.K. could cost as many as 750,000 lives, the report said. It also claimed major coastal floods would likely need a military evacuation of hundreds of thousands of people.

Terrorism minister Adm. Alan West, a former head of defense intelligence, said a new focus on climate change and disease comes as the threat of terrorism in Britain eases somewhat.

"I can put my hand on my heart and say that in the last year, though the risk hasn't gone away, we are safer than we were a year ago," West told BBC radio.

But staff at MI5, Britain's domestic spy agency, will increase from 3,000 to 4,000, to help combat an estimated 2,000 potential terrorists in the United Kingdom, Brown said.

Resources and technology at the government's secret eavesdropping center also will be enhanced, in part to respond to a new threat from cyber attacks, he said.