ALEXANDRIA, Va. â€"  An alleged white supremacist from Virginia was arrested Wednesday after he purportedly obtained a fully automatic AK-47 and expressed support for violence toward political figures including President Barack Obama and Attorney General Eric Holder.

The Justice Department said Douglas Howard Story, 48, was charged with making a firearm in violation of the National Firearms Act, which carries a penalty of up to 10 years in prison.

A source alerted authorities after Story, of Manassas, Va., posted information on a website indicating he was preparing to buy an AK-47 and have it modified to become fully automatic, a Justice Department statement said. He allegedly said he was planning to ambush and murder any law enforcement officer who stopped him on the street if martial law was enacted in the US.

Story also made statements on various white supremacy internet forums under the name "Confederate Brother." He allegedly ranted about his hatred of minorities and expressed a desire for Obama and Holder to be removed from office "with a 30.06," likely referring to a rifle round.

According to court records, Story provided a semi-automatic AK-47 and $120 to undercover law enforcement with the intent of having the weapon modified to become fully automatic, the Justice Department said. He was arrested Wednesday afternoon by members of FBI Washington Field Office's Joint Terrorism Task Force after allegedly receiving the modified weapon from an undercover agent.