Chinese Internet surfers play online games on their computer stations at an Internet cafe in Beijing

Reporters Without Borders says several governments in Asia are among the world's worst "enemies" of Internet freedom, because they increasingly censor Web sites and jail dissidents who publish their views online.

Half of the countries Reporters Without Borders calls "enemies of the Internet" are in Asia, and China tops the list.

The media advocacy group says China not only has put in place the world's most sophisticated mechanisms to block access to information, but it also has by far the highest number of imprisoned cyber-dissidents.

Jef Julliard, an editor for the organization in Paris, says 48 of the 60 people currently in jail for publishing their views online are Chinese.

"There is no other country in the world where some people can be jailed and sentenced for very heavy prison terms, like 10 years in prison, only because they published some critical stories, articles or reports on the Internet asking for more democracy in their country," said Julliard.

Reporters Without Borders also criticizes the U.S. Internet company Yahoo! for allegedly cooperating with Chinese authorities, which led to the arrest of four cyber-dissidents.

The Internet has become a powerful tool in countries in Asia where press freedom is curtailed. It has given a growing number of people access to alternative sources of information and has provided many with a venue to freely express their views for the first time.

But Roby Alampay, executive director of the Southeast Asian Press Alliance in Bangkok, says while advances in information technology have helped many people in the region, the Internet remains a vulnerable medium.

"Because at the same time that individuals and organizations are discovering the potency of this, so are governments, who retain their interests in trying to keep information censored and under their control," said Alampay.

Among other governments in the region that feel most threatened by cyberspace are the rulers of Vietnam, Burma, Nepal and North Korea. Authorities there censor independent news sites and opposition publications and monitor the Web to stifle dissent.

Reporters Without Borders says that some other countries in the region that have so far respected online freedom need to be closely watched for signs of censorship.

Among those on the organization's watch list are Malaysia, South Korea and Singapore.

Alampay says that Singapore has warned Internet users ahead of next week's elections that it will not tolerate any political discussion on the Internet.