BEIJING -- Google Inc. said Friday that it would step up efforts to stop pornography reaching users in China after a mainland watchdog found the search engine turned up a large number of links to obscene and vulgar sites.

"We have been continually working to deal with pornographic content, and material that is harmful to children, on the Web in China," a statement from the company said.

It added that it had renewed efforts to keep the Internet in China clean after noticing criticism posted Thursday to the Web site of the mainland watchdog, the China Internet Illegal Information Reporting Center.

The watchdog said that despite official warnings, Google was still failing to "filter pornographic contents from its search engine results according to China's relevant laws and regulations." It said tests found that the search engine provided links to a large number of lewd and vulgar pictures, videos and articles, though it gave no specific examples.

China, which has the world's largest population of Internet users at more than 298 million, also has one of the world's tightest controls over the Internet. The government bans online pornography and this year launched a nationwide crackdown that led to the closing of more than 1,900 Web sites.

Google, headquartered in Mountain View, California, has struggled to expand in China, where it says it has about 30 percent of the search market. China's homegrown Baidu search engine remains the most popular, with about 60 percent of the market.