Alleged Chinese cyberattacks on U.S. and German government computers are part of an espionage strategy aimed not just at gaining intelligence but causing disruption and embarrassment, Western officials and experts say.

In the past 10 days, Beijing has hotly denied reports in Western media that Chinese hackers penetrated systems in the Pentagon and in the chancellery and key ministries of German leader Angela Merkel.

On Wednesday, Britain's Foreign Office declined to comment on a report in the Guardian newspaper that its network had also been hit, but a security source confirmed there had been frequent Chinese attempts to penetrate British government systems. "They're interested in scientific and technological information, both civil and military-related. They're interested in acquisition of political and economic intelligence. And they're interested in monitoring of dissident individuals and groups," the official told Reuters.

"Part of that is acquisition of information through cyber-attack."

While declining further specific comment on China, he said cyber-attacks in general had several possible aims besides gaining secret information. They can severely disrupt the target's networks and damage its reputation, especially in the case of a high-profile institution like the Pentagon.

"Hacking into the home of Fortress America is quite a reputational hit," the official said.

The Pentagon said on Tuesday that computer hackers had gained access to an unclassified e-mail system in the office of U.S. Defense Secretary Robert Gates, but declined to comment on a Financial Times report that the Chinese army was reponsible.

It said there had never been any threat to classified systems or disruption to defence operations.

In Germany, Der Spiegel magazine reported last week that the domestic federal intelligence service told the government in May that Chinese hackers had penetrated ministry networks using so-called Trojan software disguised in Word or Powerpoint files.

The spy programmes were detected in the chancellery and the foreign, economic and research ministries, it said.

China has rejected both the U.S. and German allegations, complaining of "wild accusations" which were "totally groundless and also reflect a Cold War mentality".

Sandra Bell, security analyst at the Royal United Services Institute in London, said the emergence of the two reports in consecutive weeks appeared to signal that Western governments were running out of patience with the alleged Chinese activity.

"It does seem the international community appears to be saying: 'We know who's doing this and we want it to stop,'" she said.