The head of US Air Force intelligence and surveillance said data available commercially through online mapping software such as Google Earth posed a danger to security but could not be rolled back.

'To talk about danger is, if I may, really is irrelevant because it's there,' said Lt Gen David Deptula, deputy chief of staff for intelligence, surveillance and reconnaissance.

'No one's going to undo commercial satellite imagery,' he said.

Deptula cited Google's Google Earth, which gives Web users an astronaut's view of the earth and allows them to zoom down to street level. He said it had provided anyone with a credit card the ability to get a picture of any place on earth.

'It is huge,' he said. 'It's something that was a closely guarded secret not that long ago and now everybody's got access to it.'

Asked if the US military might try to implement restrictions or blackouts on imagery of some areas, Deptula said he was not aware of such an attempt.

'I don't want to speak to specifics, but not that I'm aware of,' he said.

Instead, governments are trying to mitigate the effect through camouflage, concealment and deception, he said, providing no other details.Reuters