The men, who are aged 36, 278 and 26, were taken to Crosshouse Hospital on Friday night for treatment.

A spokeswoman for Strathclyde Police said none of the men was in a life-threatening condition.

One man was detained overnight for treatment.

Alex Neil is calling for an inquiry

A fourth man has been charged in connection with the alleged incident, which took place in a recreation area of the jail at about 2100BST on Friday.

Critics of the Kilmarnock jail - Scotland's only private prison - have renewed calls for an inquiry into the way that the facility is run.

Scottish National Party MSP Alex Neil said: "I've predicted for long enough that the way in which Kilmarnock prison is run, which is for profit, is going to lead to a disaster in terms of prisoner safety and public safety.

"What we need now is an urgent inquiry.

"I think the time has come for the Scottish Executive to review the contract with Premier Prison Services to see if it is at all possible to legally terminate it and bring the prison back into public ownership."