A congressional hearing on Yahoo Inc., Google Inc. and other U.S. Internet companies has intensified the debate over the self-censorship in China, prompting the U.S. government to investigate deeper into the issue.

On the hearing in Washington on Wednesday, representatives of the world’s leading internet service giants- Google, Yahoo, Microsoft and Cisco Systems- were presented. They were criticized by U.S. lawmakers from both parties for agreeing to help Chinese authorities by censoring Internet searches, which would jeopardize the rights of Chinese citizens to access information, according to the Associated Press (AP).

An evangelical Christian group Focus on the Family quoted the comments from the U.S.-based Chinese Christian persecution watchdog China Aid Association (CAA) on the issue. The chairman Bob Fu said Chinese Christians were among the internet savvy. Among 100 million internet users in China, many of them are Christians who depend on the internet for spiritual food, he said. The self-censorship will therefore have great impact on them.

"Christians are forming internet chatting rooms do discuss the gospel, their church. It’s been increasingly influential to the ministry of the gospel in China," he added.

Apart from politically sensitive search words such as "Human rights in china" in Chinese, "Rights defenders" in Chinese, "Chinese Communist Party" in Chinese, "Tiananmen Square", the list of censored words includes Christian "God" and "Christ".

Amid strong criticism, the U.S. Internet companies unveiled the dilemma they have encountered in expanding their services to China and other countries with restrictive policies on free speech.

"All U.S. and international firms operating in China face the same dilemma of complying with laws that lack transparency and that can have disturbing consequences inconsistent with our own beliefs," Yahoo spokeswoman Mary Osako said in a statement.

On Google’s online journal, senior policy counsel Andrew McLaughlin urged the U.S. government to "treat censorship as a barrier to trade" and to bring up such concerns as part of bilateral diplomatic talks, AP reported.

Microsoft and Yahoo also released a joint statement last month calling on the US government to help solve censorship problems in China.

Even though the flow of information to Chinese citizens is still under certain control under the self-censorship policy, the internet companies believe that "cooperation with China enabled the Internet to flourish and mostly advance the flow of information to the Chinese people," according to Bloomberg news.

"On balance, it's better for Microsoft and other Internet companies to be engaged in China," Microsoft Associate General Counsel Jack Krumholtz was quoted as saying. "The benefits far outweigh the downside in terms of promoting freedom of information."

On Tuesday, the U.S. State Department established a task force to investigate the problems posed to the Internet by repressive regimes. The task force is expected to push other governments to grant more freedom in the flow of information, Josette Shiner, said an undersecretary of state.

The debate was first initiated when Google. Inc announced to launch Google.cn- a Chinese-based version of Google search engine- last month. The New York-based group Human Rights in China (HRIC) revealed that many "sensitive" search results are blocked by Google.cn to prevent them reaching Chinese Internet users.