A Chinese government watchdog has ordered Yahoo China to clean pornographic content from a photo-sharing site it hosted, a reminder of the regulatory challenges often faced by foreign Internet companies in China.

The government-linked Internet Society of China on Friday said Yahoo China and other local Web sites had "violated social morals" by allowing porn to appear on their domains. The same group censured Google earlier this year in a row over pornographic search results that ultimately led authorities to block Google.com and Google Apps for a few hours across China.

The criticism of Yahoo China, also called China Yahoo, gave no hint that such escalation was likely. The offending service, a user-generated blog and photo album site called Yahoo Space in Chinese, was closed at the end of last month, said a spokesman for Alibaba Group, a local e-commerce group that owns Yahoo China. Alibaba is restructuring Yahoo China to focus on entertainment features.

Chinese authorities patrol the Internet for porn, sensitive political discussions and other content deemed illegal or harmful. Owners of search engines, blog services and other sites are expected to censor such content themselves and can face punishment for failing to do so.

Google defused its tension with the government by changing the algorithm on its China search engine to block problematic search results. Google sites did not appear on the watchdog's newest list.

China has shuttered thousands of Web sites and arrested dozens of people this year in a campaign against porn and other online content.