The U.S. Department of Justice has launched a criminal probe into an anti-ICE protest that tore through a Minnesota church service Sunday … and former CNN host Don Lemon could be swept up in it under the century-old “KKK Act.”

DOJ Assistant AG for Civil Rights Harmeet Dhillon tells TMZ … every demonstrator who stormed the Sunday service at Cities Church in St. Paul is now under federal investigation. When we asked if Don is in the crosshairs, Dhillon wouldn’t confirm or deny it, telling us to connect the dots ourselves.

Don says he was merely doing his job — reporting a news story from the scene. But, on his livestream, Don is seen kissing the organizer of the protest on the cheek, which the feds might interpret as him having a closer connection to the group.

Dhillon says FBI agents are already talking to witnesses, and while no formal charges have been filed yet, it’s “fair to say” charges are coming under the Face Act and KKK Act, that make it a crime to terrorize and violate the civil rights of citizens.

Lemon live-streamed the chaos as anti-ICE activists interrupted the service to protest federal immigration raids in Minnesota — part of a backlash after an ICE agent shot and killed Renee Good earlier this month. The pastor of Cities Church has been accused of being a senior ICE official.