LITTLE ROCK, Ark. -- Guards at two prisons in Arkansas were assaulted by inmates in separate attacks on Thursday and hospitalized, the latest in a string of violent incidents at the state's correctional facilities that have included officers being held hostage by prisoners.

The Department of Correction said two officers were assaulted by several inmates at the Varner Unit in Grady, about 70 miles (113 kilometres) southeast of Little Rock. One guard suffered multiple lacerations and the other a single injury that officials did not elaborate on. The officer with the single injury was treated and released from an area hospital, while the other guard remained hospitalized Thursday night.

The assault occurred a little more than two hours after a guard at the Maximum Security Unit in Tucker, 30 miles (48 kilometres) southeast of Little Rock, was assaulted by an inmate. That guard sustained multiple injuries to the face and head, and was being treated at an area hospital. The department did not release the names of the inmates or the guards.

Department spokesman Solomon Graves said the two assaults appeared to be unrelated. It was not immediately clear what prompted the incidents. The inmates in both attacks were moved to restrictive housing, he said. Graves later said that several inmates at Varner who had barricaded themselves in a barracks after the assault on the guards were sent to area hospitals for evaluation and treatment after the department used nonlethal force on them.

The Maximum Security Unit, also known as Tucker Max, is the same facility where several inmates last month held three officers after taking their keys and a Taser. They released them after three hours and surrendered.

In another incident, a guard at Tucker Max fired three warning shots into the air in July after two guards and an inmate were attacked there.

The violence at Arkansas' prisons has prompted investigations by the Correction Department and State Police. Three inmates were injured earlier this month at the Cummins Unit in Grady after a disturbance that included prisoners breaking windows and damaging surveillance equipment. Officials are also investigating an inmate's death last month that stemmed from an assault in July at the Tucker Unit, which is a different facility than Tucker Max.

State Police last month said they had more than two dozen open cases involving assault or battery by inmates on guards or fellow inmates. A State Police spokesman did not have an updated number of incidents under investigation Thursday.

Gov. Asa Hutchinson has said he expects disciplinary action will be taken against employees at the Maximum Security Unit after the July and August incidents, but that he still has confidence in Correction Department Director Wendy Kelley. A spokesman said Hutchinson was waiting on additional information about Thursday's assaults and did not have a comment.

Kelley told lawmakers last month that both previous incidents at Tucker Max began when inmates managed to escape solitary fenced-in areas during their recreation breaks.

The department has said it will replace the chain-link recreation areas and has taken temporary steps to strengthen the cages at the unit, along with adding more security measures during recreational periods.

Varner is one of four prisons where Arkansas lawmakers approved raising hazard pay for officers and employees, a move correction officials said was needed to fill vacancies.

A lawmaker repeated her call for answers from prison officials on what's caused the recent disturbances after Thursday's assaults.

"Apparently something is not being attended to and we need to know what it is," said state Sen. Joyce Elliott, who co-chairs a legislative committee that oversees prisons. "This has gotten to be an issue of safety for everybody concerned within the system."