The U.S. Justice Department says four men have been arrested for an alleged plot to buy explosives and produce the deadly toxin ricin to attack citizens and the government.

In a statement, the U.S. Attorney for the Northern District of Georgia said two of the men sought to buy explosives and a silencer, while the other two took steps to produce the toxin.

U.S. Attorney Sally Quillian Yates said the four men — who range in age from 65 to 73 years old — are from the U.S. state of Georgia and suspected of being part of a fringe militia group.

She said that while there is a focus on the threat from violent extremists abroad, this case demonstrates the need for vigilance in protecting the country from citizens within who seek to do harm.

Authorities said the men met to discuss attacking various government officials and targets, and that those meetings were monitored by a confidential source who was working with federal officials.

The four men are to appear in court Wednesday.