The paper accused the US of exploiting social media, such as Twitter and YouTube, to foment unrest in Iran.

"We're afraid that in the eyes of American politicians, only information controlled by America is free information, only news acknowledged by America is free news, only speech approved by America is free speech, and only information flow that suits American interests is free information flow," it said.

Some commentators and observers are worried the war of words will hurt ties between China and the US.

Reuters said the case was "raising the stakes in a dispute that has put Google in the middle of a political quarrel between the two global powers".

"The dispute has stoked friction between Beijing and Washington, already wrestling over trade, US weapons sales to Taiwan and human rights."

The Wall Street Journal said Washington, which "has started to talk about the seriousness of the problem", now "needs a plan to fix it".

But Chinese analysts said the impact of the case has been exaggerated, and that it would not harm Sino-US relations in the long term.

"The Google case reflects a new (cyber) problem, which is just rooted in old differences between the two countries," said Niu at Peking University.

He said Beijing and Washington differ on "recogni-zing what freedom of speech is".