BIG STONE GAP, Va. (AP) — An attack by inmates at a Virginia prison injured five guards, according to state corrections officials who said most of the assailants were MS-13 gang members who entered the U.S. illegally.

Three guards were stabbed and were transported for medical treatment along with two others hurt Friday at Wallens Ridge State Prison in western Virginia, the state Department of Corrections said.

The agency said in a press release that six inmates involved had all been convicted of violent crimes including murder and rape and that five of them were “confirmed MS-13 gang members from El Salvador, who were in this country illegally.” It said the sixth inmate was a U.S. citizen with ties to a different gang.

“Five of the individuals responsible for this senseless attack should never have been in this country in the first place,” Chad Dotson, director of the Virginia Department of Corrections, said in a statement. “Every single day, our officers put their lives on the line to ensure public safety. … This attack is an example of the dangers they face when they show up to work every day.”

Corrections officials gave no further details about the prison attack, citing an ongoing investigation.

The agency said three of the injured officers were treated and released the day of the attack. The remaining two were hospitalized in stable condition.

Carla Miles, a Department of Corrections spokesperson, said she did not know if the two guards remained in the hospital Sunday.