A federal grand jury in central Illinois on Wednesday returned a superseding indictment that brings additional charges against four men previously indicted on weapons charges — three of whom are awaiting trial in a Minnesota mosque bombing case.

Michael Hari, 47, Michael McWhorter, 29, Joe Morris, 22, and Ellis Mack, 18, now are also charged with conspiracy to interfere with commerce by threats and violence. Hari, McWhorter and Morris also are charged with attempted arson, and Hari is charged with possession of a firearm by a felon.

It wasn't immediately known if the men have lawyers representing them on the new charges.

Hari, McWhorter and Morris are charged in Minnesota with bombing the Dar al Farooq Islamic Center in Bloomington last August. The explosion caused fire damage, but no injuries.

The indictment from the grand jury in Springfield alleges the three men and Mack conspired from August 2017 to March 10, 2018, to affect commerce by robbery and extortion. The men allegedly robbed or attempted to rob Walmart stores in Illinois, attempted to extort Canadian National Railway by threatening to damage tracks in Illinois if the railroad didn't pay ransom, and robbed or attempted to rob individuals in Indiana suspected of being involved in drug trafficking.

The indictment also alleges that in November 2017, Hari, McWhorter and Morris attempted to damage the Women's Health Practice in Champaign, Illinois, using fire and explosives.

Prosecutors contend the four formed a militia group that eventually identified itself as the "White Rabbits." According to the indictment, the group obtained materials used to make explosives, provided weapons and uniforms to group members, and assigned ranks to its members. Prosecutors allege the materials and other items belonging to the group were kept in a building in Clarence, Illinois.

Hari, Morris, McWhorter and Mack are all from Clarence. All four have been ordered to remain in the custody of the U.S. Marshals Service, according to the U.S. attorney's office.