The White House is warning TV networks Osama bin Laden may be using them to secretly communicate with associates.
Officials are asking US networks to "exercise judgment" in broadcasting his videotaped messages.
The broadcasts may contain messages "that could be a signal to terrorists to incite attacks," said White House spokesman, Mr Ari Fleischer.
Mr Fleischer said he has no "hard indications" that such communication is embedded in the videotaped messages that have been aired by networks in recent days.
But he said the means of communications from Afghanistan to the outside world are limited: "One way to communicate outside Afghanistan to followers is through Western media.
"At best, Osama bin Laden's messages are propaganda calling on people to kill Americans. At worst, he could be issuing orders to his followers to initiate such attacks," Mr Fleischer said.
He said he knew of no similar calls to news executives outside the United States, or to newspapers or other media in this country.
Secretary of State Mr Colin Powell said analysts were looking at the statements, including one made on Tuesday by al-Qaeda spokesman Abu Ghaith praising the terror attacks on the United States and warning there would be more.