The FBI, spurred in part by this week's unusually menacing audio message from Ayman Al-Zawahiri, today advised state and local law enforcement officials to expect an increase in Al Qaeda propaganda messages aimed at inciting followers to commit terrorist acts.

FBI and counterterrorism officials stressed today that they have no fresh intelligence about any specific threats—one reason why today's FBI intelligence bulletin, issued in conjunction with the Department of Homeland Security, was blandly worded and low-key in tone.

But privately some analysts are worried about the blunt new message from Zawahiri, the deputy to Osama bin Laden. "It's a little spooky," said one senior official. Seeking to exploit a worldwide Muslim backlash over recent Israeli bombing strikes in Gaza, Zawahiri exhorted followers to "attack the interest of the Jews and the Americans." He then added, "Select your targets, collect the appropriate funds, assembly your equipments, plan [your attacks] accurately, and then charge toward your targets … There is no place today for those who claim that the battlefield with the Jews is limited to Palestine."

Counterterrorism officials and analysts have been debating for the last few days whether Zawahiri's directive to "select your targets" was a direct command to operatives in the field or a more general incitement to sympathizers.

Evan Kohlmann, a government counterterrorism consultant who studies Al Qaeda messages, says the new tape seemed "palpably different" from Zawahiri's usually fiery anti-American tirades. "It's quite rare that he would be this direct and blunt about it," Kohlmann says. "My personal opinion is when he said this"—referring to the "select your targets" line—he "wasn't talking in the abstract, he was saying, 'We're doing it.' It was very much a call to arms."

But counterterrorism officials say that they have no idea what "it" might be—or any hard indicator that a major Al Qaeda strike is imminent, at least not in the United States. There has been no spike in terrorist "chatter" picked up by U.S. surveillance in recent weeks or recent arrests suggesting an operation might be underway, said one official who asked not to be identified talking about intelligence information.