The United States and Britain called on June 4 for international cooperation against threats to cyber security following a fresh spate of attacks on government and corporate targets.

US Defense Secretary Robert Gates and British Defence Secretary Liam Fox underscored the urgency of the problem at an Asia-Pacific security forum in Singapore also attended by their Chinese counterpart Liang Guanglie.

China denies being the source of attacks on US security systems and the two western officials deliberately avoided singling out Beijing.

Liang is scheduled to address the Singapore conference tomorrow.

Gates said "we take the cyber threat very seriously and we see it from a variety of sources, not just one or another country."

Fox said London will host an international conference on the "war of the invisible enemy" later this year.

"The effect on the economies of this region of a well-planned and well-resourced cyber attack on transnational commercial networks and institutions would be catastrophic, and would impact on us all," he said.

"Cyber attacks are already happening in large numbers and on a regular basis ... which is why we want to convene a proper international conference to see how we can deal with it."

The London talks will include discussions on a potential legal framework, Fox said.

Just days before the Singapore forum, Internet giant Google said a cyber spying campaign originating in China had targeted Gmail accounts of senior US officials, military personnel, journalists and Chinese political activists.

China said Thursday it was "unacceptable" to blame it for the incidents.

Gates said "serious international tensions" could be avoided if there were rules "that let people know what kinds of acts are acceptable, what kinds of acts are not, and what kinds of acts may in fact be an act of war."