BEIJING  As the Chinese government expands what it calls a campaign against pornography, cellular companies in Beijing and Shanghai have been told to suspend text services to cellphone users who are found to have sent messages with “illegal or unhealthy content,” state-run news media reported Tuesday.

China Mobile, one of the nation’s largest cellular providers, reported that text messages would automatically be scanned for “key words” provided by the police, according to China Daily, a state-controlled English-language newspaper. Messages will be deemed “unhealthy” if they violate undisclosed criteria established by the central government, the newspaper said.

The increased surveillance of text messages is the latest in a series of government efforts to severely tighten control of the Internet and other forms of communication.

Since late last year, China has closed hundreds of Web sites, including popular file-sharing sites, and limited its citizens’ ability to set up personal Web sites.