"The attack on our corporate infrastructure and the surveillance it uncovered - as well as attempts over the past year to limit free speech on the web even further - led us to conclude that we are no longer willing to censor our search results," she said.

Commenting on the future of Google's operations in China, Wong said the company was "firm in our decision that we will not censor our search results in China and we are working towards that end".

"We are firm in our decision that we will not censor our search results in China and we are working towards that end"

Nicole Wong,
Google vice-president

She added that Google has "many employees on the ground" in China, "so we recognise both the seriousness and the sensitivity of the decision we are making".

Wong gave few new details on the mid-December cyber attack thought to have originated from China that was partly responsible for Google's threat to pull out of the country.

However, she said the company was in discussion with the Chinese government as to how it can continue to do business in the country.

China has so far insisted that all companies offering internet services in China must comply with regulations requiring them to block access to sites deemed undesirable by Chinese censors.

"We want to get to that end - of stopping censoring our search results - in a way that is appropriate and responsible," Wong told the hearing.

"We are working on that as hard as we can but it's a very human issue for us."

Tuesday's senate subcommittee hearing was chaired by Dick Durbin.

The Illinois Democratic senator has said he intends to introduce a bill that would require internet companies to follow a code of conduct for doing business in countries that restrict free speech and human rights.

Durbin's proposed bill would subject companies that do not take "reasonable steps to protect human rights" to civil or criminal penalties.