Joe Harris, left, and Donovan Cobbs are shown in these Arkansas Department of Correction photos.

Two inmates were found unresponsive in their cells Wednesday morning at the state’s highest security lockup, an Arkansas official said, raising the total number of deaths at the prison this week to five.

The deaths at the Varner Unit are under investigation by the Arkansas State Police, but Jim DePriest, the chief attorney for the Department of Correction, said it would “not surprise” officials if the deaths are determined to be drug-related.

DePriest identified the prisoners who died Wednesday morning as Donovan Cobbs, 26, who was serving a 10-year sentence for robbery; and Joe Harris, 55, who was serving a life sentence for aggravated robbery.

Three other men died Sunday and Monday morning. Edward Morris, 34, was pronounced dead at 10:35 a.m. Sunday, DePriest previously said. Stephen Kantzer, 38, and Marlon Miles, 41, were pronounced dead around 1:30 a.m. Monday.

Stephen Kantzer, 38, and Marlon Miles, 41, are shown in these Arkansas Department of Correction photos. No photo was available of Edward Morris, 34.

The state prison system has struggled to stem the flow of drugs, especially a volatile form of synthetic marijuana known as K2, into prisons over recent years.

According to internal reports, corrections officers found suspected K2 near the body of an inmate who died over the weekend.

Miles and Morris were housed in separate cells at Varner Supermax, the state's highest-security lockup, officials previously said. Kantzer was housed in general population at the other side of Varner, which is 28 miles south of Pine Bluff off U.S. 65 in Lincoln County.

In response to the five deaths, DePriest said the department was conducting a unit-wide “shake-down” at Varner in hopes of finding and seizing illicit drugs.

Close to a dozen other inmates have been treated at Varner for suspected drug-related illnesses in recent days, according to the spokesman.

Through July, DePriest said, there were 468 K2 incidents, which can range from locating the drug to discovering someone under the influence, which puts 2018 to be on track for about 350 fewer than 2017.

Gov. Asa Hutchinson said Wednesday on Twitter that he had been notified of the deaths and was monitoring the investigation as new information became available. In the meantime, he requested that Department of Correction Director Wendy Kelly study best practices from other states for preventing the use of K2 to ensure the safety of those in state custody.

In June, Kelly testified to lawmakers that the "vast majority" of drug-related incidents at correctional facilities involved K2. She said the department was instituting several policy and educational changes in an effort to reduce K2 incidences, which peaked at 1,136 last year.

Department spokesman Solomon Graves said K2 can be smuggled in through the mail. The agency's new mail policy limits correspondence to photocopies of the first two pages of letters, a policy Kelly called "very unpopular" in June, but which DePriest has said could be partly responsible for a decline in K2 incidences.

Prisons have also installed new body scanners, which all visitors and staff must pass through. DePriest said the department has instituted educational policies in facilities to warn inmates and visitors of the dangers of the drug.

Medical staff members are on alert in all units, DePriest said, but while overdose-reversing drugs are helpful with respect to opioids, the compounds in K2 likely would not be affected by emergency treatment drugs like naloxone.

Officials in Ohio and Pennsylvania said staff members at prisons in those states have been treated for exposure or suspected exposure to drugs. It is not clear whether the incidents in those states were related to each other or to the incidents at Varner.

Read Thursday's Arkansas Democrat-Gazette for full details.