Washington - US trade officials sent a letter to their Chinese counterparts Wednesday urging them to revoke an order that requires a controversial internet filtering software to be installed on computers.

The Green Dam software, which China will require on all new computers from July 1, could be used to restrict free speech and raises questions about free trade, US Trade Representative Ron Kirk and Commerce Secretary Gary Locke said in a letter to the Chinese government.

"China is putting companies in an untenable position by requiring them, with virtually no public notice, to preinstall software that appears to have broad-based censorship implications and network security issues," Locke said in a statement.

China's government has said the software is needed to protect children from pornographic material and will apply to any company that wants to sell computers in the country.

The US said that the rule may violate China's obligations under the World Trade Organization, by forcing one specific software to be installed on computers.

The technology could also be used to consolidate existing blocks on politically sensitive websites, and the United States has said there are better avenues for blocking pornography.

There have been security concerns that the software could allow remote monitoring and control of users' computers and the theft of personal information.

"Protecting children from inappropriate content is a legitimate objective, but this is an inappropriate means and is likely to have a broader scope," Kirk said.(dpa)