(CNN) -- The number of American "patriot" extremist groups has reached a record level, according to a new study, and experts are warning of a wave of anti-government violence.
A report released Tuesday by the Southern Poverty Law Center counted 1,360 "patriot" extremist groups in 2012 -- up by 7% from 2011. The study defines patriot groups as anti-government militias driven by their fear that authorities will strip them of their guns and liberties.
"They believe the Constitution is being raped. With hate groups, things are going to get worse because they feel like they're in battle," said David Gletty a former FBI informant who spent time undercover with various militia and extremist groups. "It's not surprising with their hatred of President (Barack) Obama that there are even more hate groups out there."
The study said California has the most patriot extremist groups, with 81.
The SPLC report also offers a bit of good news: The number of "immigrant-bashing" extremist groups -- so-called nativism organizations -- is way down from 2011, falling by 88%.
The new statistics come after a string of crimes linked to extremist groups. A year ago, a Michigan militia leader and his son pleaded guilty to federal gun charges. Last August, a 40-year-old ex-soldier-turned singer for a white supremacist rock band shot up a Sikh temple in Oak Creek, Wisconsin, killing six people, before taking his own life. A few weeks later, a group of Georgia men was linked to an anti-government militia plot to assassinate Obama.
Obama's election as the first African-American president and his pro-gun control stance have fueled the increase in anti-government groups, according to the report.
"We are seeing a huge reaction to the potential for gun control, and that reaction is so angry that it's hard not to be afraid of what's coming down the road," said Mark Potok of the SPLC.
Domestic terror: Are we doing enough?
The rise in such groups echoes a period almost 20 years ago, around the time when Congress passed the 1993 Brady Bill and the 1994 ban on assault weapons, the SPLC said. That legislation came near a period of infamous and deadly anti-government violence in Waco, Texas; Ruby Ridge, Idaho; and Oklahoma City, "and led to the first wave of the patriot movement," the report said.