An inmate already awaiting trial for strong-arm robbery faces new charges after he allegedly injured two correctional officers during a standoff at the Butler County Prison, authorities said.

Butler County detectives Wednesday charged Clifford J. Anderson, 32, of Pittsburgh with felony assault in connection with last week’s jailhouse fracas.

The altercation began shortly before noon May 19 when prison officers moved to place the restricted housing unit in lockdown.

But Anderson and inmate Dontay R. Green, 27, of Pittsburgh refused to comply with orders, according to court documents.

The captain on duty tried to defuse the problem but Anderson and Green “decided to make a stand,” Pat Cannon, chief county detective, said in charging documents.

The captain ordered all available correctional officers to help. When the suspects would not back down, officers fired pepper ball guns at both.

Anderson picked up two plastic chairs and “used them to threaten the responding officers,” documents said. The officers rushed both inmates and took them to the floor,

Cannon said two officers were injured trying to subdue Anderson.

One of the injured officers was taken to Butler Memorial Hospital and later diagnosed with a dislocated wrist; the other officer suffered minor bruises.

Anderson is charged with aggravated assault and resisting arrest. Green is charged with resisting arrest.

Anderson has been in prison since his arrest on charges lined to an armed holdup in Butler on July 14, 2010.

Butler police arrested Anderson and two other men after they allegedly robbed a man outside a Fourth Avenue home. The victim said Anderson had a gun, police said.

Anderson remains in the prison on $150,000 bail.

Meanwhile, Green is in the prison on $30,000 bail in connection with a felony drug case in Butler in December 2010.

Court records showed that trials for both suspects are pending.