LEWISBURG — A U.S. Penitentiary at Lewisburg staff member was assaulted by two inmates and four officers were injured responding to the attack Sunday morning, the second violent incident at the prison in less than a week.

An unidentified staff member suffered two puncture wounds to the lower back and superficial wounds across the chest and lower abdomen in the 7:50 a.m. assault by two inmates, according to a statement released by prison spokesman Scott Finley.

Four officers who responded to the attack were also hurt and required medical treatment, one for a knee injury, one for a rib injury, another for an elbow injury and the fourth for a cut on the elbow, the statement said. The two inmates were treated at the prison for abrasions.

The statement did not say what type of weapon was used by the inmates, and no other details were released.

Finley said the prison remains secure and is operating under a lock-down status.

It was the 45th violent incident at the prison this year and is being investigated by the FBI. The most recent attack occurred on Tuesday, when an inmate stabbed a guard in the thigh with a spear made of rolled-up newspaper and magazines and a metal tip held on with dental floss .

“It’s unfortunate to say, but I wasn’t surprised,” said Tony Liesenfeld, secretary/treasurer of the American Federation of Government Employees Local 148.

The union has complained for months that inadequate staffing is putting officers at risk.

Liesenfeld, who met the guards at the hospital where they were treated early Sunday, said each of them “acted appropriately” and attributed the assault to the lack of adequate staffing.

“Hopefully we can get this situation addressed before someone is killed,” he said, adding that local management has echoed the union’s request for more staff.

There are presently 264 guards at the penitentiary, overseeing 1,089 inmates, many of whom are among the country’s most violent prisoners. Inmates are held up to 23 hours a day in a cell.

Due to the low number of staff, Liesenfeld said, each prisoner is escorted to and from the cell by a single guard, even though similar prisons across the country employ up to three guards per inmate for the same task.

It also limits the frequency of cell searches, he said.