FBI Offices Told to Boost Surveillance of Terror Suspects in Wake of Paris Attacks.

— -- FBI leadership has told offices across the country to boost surveillance of terrorism suspects in the wake of Friday’s deadly attacks across Paris, hoping to guard against any related violence in the U.S. homeland, ABC News was told.

In a conference call late Friday with the heads of the FBI’s 56 field offices, the message was clear: "Make sure you know where everyone is," according to one source with knowledge of the conference call.

Top FBI officials hosting the call emphasized there are still many unknowns about the attacks in Paris, where terrorists killed at least 129 concertgoers, sports enthusiasts, evening diners and others in a coordinated assault. But what is known about the attack is troubling, so FBI leadership urged field-office chiefs to keep even tighter tabs on anyone in their areas who they believe has been consuming terrorist propaganda and may be inspired to act in the wake of the tragedy in Paris, according to sources with knowledge of the conference call.

ISIS has already claimed responsibility for the Paris attacks, and FBI Director James Comey has said there may be as many as thousands of people inside the United States consuming online "poison" from the group.

The FBI is investigating such terror suspects in every single U.S. state, Comey said. Surveillance of those suspects is a resource-heavy endeavor, each requiring contributions from perhaps dozens of agents.

In the past two and a half years, nearly 90 Americans have been charged with plotting ISIS-inspired attacks inside the United States or are otherwise suspected of supporting the terrorist group in some way.

Nevertheless, U.S. authorities "know of no specific or credible threats of an attack on the U.S. homeland of the type that occurred in Paris," DHS Secretary Jeh Johnson said in a statement.

In the FBI conference call overnight, the assistant-directors-in-charge and special-agents-in-charge of the FBI field offices were also urged to maintain a "flow of information" with state and local law enforcement, and the division chiefs were told to ensure open communications with faith-based leaders, particularly those in Muslim communities.

"They want you to ... make sure everyone is on the same page, and [that you] pass out as much information as you can," one source with knowledge of the call said.

In cities across the country, state and local authorities are boosting security at many high-profile sites. And so-called "fusion centers" -– which collect and share information between federal, state and local law enforcement –- are actively monitoring developments abroad and inside the U.S., separate statements from several state agencies indicated.

As for the response from Muslim leaders, the Council on American-Islamic Relations said in a statement Friday that it condemns all acts of terrorism, calling the attacks in Paris "savage and despicable."

Meanwhile, a U.S.-based team of FBI agents –- including bomb techs, intelligence analysts and victim assistance personnel -– are on "standby" and ready to fly to Paris should French authorities ask for further assistance. Any such personnel would likely come from the FBI's New York field office, according to an official briefed on the plans.

A handful of FBI agents stationed in the U.S. embassy’s "legal attaché" office in Paris is already offering any help they can, ABC News was told.

ABC News' Josh Margolin contributed to this report.

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