The US and its Nato allies must collaborate more intensely to fend off the threat of cyber- attacks in the aftermath of the alleged Chinese assault on Google, establishing shared warning systems and broadening government contacts, the Pentagon's top cyber strategist has warned.

In an interview with the Financial Times, William J. Lynn, US deputy defence secretary, said America and Britain had been working to counter the growing international danger of cyberattacks. But he warned the US, UK and other states must deepen cross-border collaboration if they were to deal with a form of warfare that ignored national boundaries.

“You can't just protect the system by defending yourself from inside your own country,” Mr Lynn said on a visit to London, where he discussed the issue with leading UK officials. “International co-operation is imperative for establishing the chain of events in an intrusion and quickly and decisively fighting back.”