Iran's police chief has warned opposition supporters against using SMS text messages and e-mails to organize antigovernment rallies.
Ismail Ahmadi Moghaddam said spreading word of such demonstrations was a crime that carried a "heavy penalty."
Cell-phone and e-mail messages emerged as a key form of communication for Iran's opposition in the unrest that erupted in Iran after June's disputed presidential election -- including to organize demonstrations and disseminate news and images.
The messages have also become an important source of information for foreign media who are banned from directly covering the protests.
Moghaddam said anyone using SMS or e-mail messages to organize opposition rallies should know their messages were being monitored.
He said it was possible to trace both sender and recipient, and he warned that anonymous proxy servers would not protect user identities.
The warning comes amid a continuing clampdown on media in the wake of the most recent opposition protests in late December, in which at least eight people died in clashes between security forces and demonstrators.
Earlier this week, authorities closed a conservative newspaper, "Hemmat," for "slander and dissemination of lies with the intention of agitating public opinion."
RFE/RL's Radio Farda reports that the Culture and Islamic Guidance Ministry has sent warnings to six newspapers including reformist, moderate conservative and economics titles: "Jamhouri-e-Eslami," "Farhang-e-ashti," "Donyay-e-eghtesad," "Rouzan," "Etemaad," and "Bahar."
The ministry said the newspapers had distorted coverage of a prominent Qom-based cleric, Ayatollah Yousof Sanei.
For over a decade, Sanei was a major religious figure, frequently cited for his views on Islamic issues.
But his support of Iran's reformist Green Movement since the June election has brought him increasingly under fire, especially by the religious establishment in Qom.
Among the newspapers receiving warnings, the most prominent is "Jamhourieh Eslami" ("Islamic Republic").
Its first editor was Mir Hossein Musavi, the current opposition leader who has insisted he would have won the election if not for massive fraud.
compiled from Radio Farda and agency reports