FBI, Homeland Security consider possible retaliations following Syria strike Counterterrorism experts prepared for threats after previous action.

 -- FBI and Homeland Security officials are consulting with national security leadership to determine how Thursday's U.S. airstrike in Syria could affect Americans domestically.

The precise response is still unclear, according to counterterrorism sources, but officials have a sense of what the retaliation concerns for such a strike have been in the very recent past.

Counterterrorism sources tell ABC News there are specific threats to consider, but that plans have been made to deal with those potential threats.

First, the Syrian government might have operatives and sympathizers in the U.S. In 2013, when the Obama administration was considering a military strike following a chemical attack in Syria, the FBI stepped up domestic surveillance and conducted a series of interviews with Syrian nationals to deter any potential acts of violence. Supporters of Iran -- including Hezbollah -- might have operatives inside the U.S., as well.

Aside from physical attacks, there is also worry about the potential of cyberattacks from Iran and Syria.

Additionally, home-grown radicals could respond to an attack on the Muslim country, which was a major concern after the U.S. bombed ISIS in Syria in 2014. Then, Homeland Security officials issued bulletins to local police to be on the alert for such activity.

Expanded security -- especially in major cities like New York and possibly transportation hubs like airports -- should be expected in the aftermath of the strikes as a result.