'Stop the Violence' members allegedly beat up roommate

Two organisers of a US group called "Stop the Violence" have been arrested after they allegedly beat a colleague and former roommate so badly he remains in a critical condition days later.

Nikole Ardeno and Emanuel Velez allegedly punched and kicked Joshua Magraff until he vomited blood, had seizures and was knocked unconscious.

The Tuesday afternoon attack came less than 24 hours after Ardeno helped lead a march for "Stop the Violence" in Washington County in western Pennsylvania.

When police arrested Ardeno soon after the alleged attack, she was still wearing a "Stop the Violence" T-shirt.

The group has now distanced themselves from the pair.

"We do not promote violence at all, and I can't believe this is going on," local leader Suzanne Kelley told the Observer-Reporter.

"I don't want the community to get a negative effect from this because they back us."

Police say Ardeno and Velez set upon Magraff because they believed he went into the unit to retrieve his possessions, but took items that were not his.

Both Ardeno and Velez have been charged with aggravated assault and conspiracy.