The scene over the weekend at a city park in Berkeley, California was chaotic, with black-masked assailants attacking non-violent Republicans at a rally, using metal pipes, kicks and punches.
But this time the thugs were not Nazis or white supremacists. Rather, they were far-left groups aimed at attacking peaceful college Republicans who were attending rally, U.S. media reported.
The group Antifa, short for anti-fascist, is perhaps one of the best known of violent left wing groups that seem to be on the rise. Among them are leftists and far leftists, but most members do not adhere to the official Democratic Party platform.
While there has been much more recent media attention toward the radical right -- Nazis, white supremacists and others -- there's been much less attention toward radical left wing groups like Antifa.
In the meanwhile, right wing fringe groups have found a way to organize through the Internet and social media, violent far-left groups are also spreading terror.
Earlier this year, Antifa grabbed major headlines by throwing Molotov cocktails and destroying over 100,000 U.S. dollars in property in protest of U.S. President Donald Trump's supporter Milo Yiannopoulos, a conservative political commentator, who was to hold a speaking event.
Last weekend, the group made national news for violently attacking peaceful Republican demonstrators in a rally at University of California at Berkeley, one of the world's most prestigious universities.
Radical U.S. fringe groups came into the spotlight earlier this month in Charlottesville, Virginia, after a violent protest by white supremacists resulted in the death of a 32-year-old woman, who was killed by a white supremacist when he plowed a car into a group of counter protesters.
The incident made global headlines and caused an uproar on social media, as well as among TV news pundits.
Experts said such political violence could become more common, spurred on by factors including the economy, the controversial Trump presidency, and a U.S. media that critics say stirs up public discord.
There are various theories on why fringe groups like Antifa seem to be on the rise. Some analysts argue that they are reacting to the rise of far-right groups who see a leader in President Donald Trump, although Trump has condemned such radical right wing groups as "evil".
Others maintain that far-left groups are simply taking advantage of an uncertain political situation in a bid to wreak havoc.
POLITICAL VIOLENCE ON CAMPUS
Naweed Tahmas, an officer with the Berkley College Republicans, told Xinhua by phone that members of Antifa are targeting him, and have hung posters of his image around campus.
Describing the weekend's rally, Tahmas said: "Initially the police blockaded the whole area to ensure that Antifa could not get in with their weapons, but once Antifa showed up, the police department stood down and allowed them to break past their security checkpoints."
Tahmas' group has been profiled in The New York Times as a rare conservative group at one of America's most liberal campuses.
"The city has lost all control to these left wing thugs. The city is in a state of anarchy and the mayor has clearly proven that he cannot govern his own city," Tahmas said.
U.S. media reported that at least five individuals were attacked. Berkeley Police's Lt. Joe Okies told The Washington Post that "13 arrests (were made) on a range of charges including assault with a deadly weapon (and) obstructing a police officer."
On Tuesday evening, House Minority Leader Nancy Pelosi condemned the "violent actions" of Antifa after the weekend's rally.
"Our democracy has no room for inciting violence or endangering the public, no matter the ideology of those who commit such acts," said Pelosi, one of the most liberal Democrats in Congress.
"The violent actions of people calling themselves Antifa in Berkeley this weekend deserve unequivocal condemnation, and the perpetrators should be arrested and prosecuted," she said in a statement.
Such violence may once again come to Berkeley next month, as a string of firebrand conservative figures are slated to come to Berkeley to speak, and some fear that could spark a major riot.
Critics said the far-left is stifling free speech in the United States, a right that is guaranteed in the U.S. Constitution.
