Manitoba RCMP say two inmates suffered significant injuries in stabbings at the Stony Mountain Institution.
Police say a 24-year-old man and a 45-year-old man were hurt on Sunday in separate attacks at the federal prison just north of Winnipeg.
Two inmates have been charged with attempted murder in the attack on the younger victim.
Another inmate is charged with attempted murder and three others have been charged with aggravated assault in the attack on the 45-year-old man.
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Police say their investigation is ongoing.