BEIJING  Expanding what the Chinese government 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 media reported on 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 the English-language China Daily 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 initiatives to tighten control of the Internet and other forms of communication. Since November, the government has closed hundreds of Web sites in the name of rooting out pornography and piracy.

Kan Kaili, a professor of telecommunications at Beijing University, called the routine surveillance of cellphone messages a violation of privacy rights and the Chinese Constitution.