Google has said it was troubled by new regulations in Vietnam that may allow the government to block access to websites and track the activities of Internet users.

"Internet users in Hanoi will soon find that they can't reach certain sites when browsing the Web at local Internet cafes," Google policy analyst Dorothy Chou said in a blog post.

Chou said Google's concern stemmed from a regulation enacted in Vietnam in April that would require all retail Internet locations to install a particular application on their servers by 2011.

"The application will likely allow the Vietnamese government to block access to websites, as well as to track user activities," Chou said.

"The implementation of an application like this one would choke off access to information for many in Hanoi -- given how popular Internet cafes are among Internet users in Vietnam," she said.

"If the regulation spreads beyond Hanoi, it will impose these vague and non-transparent restrictions on users all over the country," Chou added.

The policy analyst recalled that Google had expressed concern over cyberattacks earlier this year on Vietnamese human rights activists and intermittent blockages of Facebook in Vietnam.

The latest regulation "is a troubling example of a government threatening free expression online and an open Internet," Chou said.

Chou's comments come after Human Rights Watch accused Vietnam of mounting a sophisticated and sustained attack against online dissent, including detaining and intimidating anti-government bloggers.

"This intensified harassment has coincided with systematic cyberattacks targeting websites operated by some of these bloggers and other activists in Vietnam and abroad," the rights group said last month.

The targets of the attacks included sites operated by Catholics criticising government confiscation of church properties, political discussion forums and an environmentalist site opposed to bauxite mining, Human Rights Watch said.