ST. PAUL, Minn. — All of the 9,500 inmates in Minnesota’s prison system were on temporary lockdown that ended early Wednesday. But state officials have offered little explanation as to why.

Authorities say the prisoners were confined to their cells and weren’t allowed to make or receive phone calls or have visitors during the 24-hour lockdown which started at 4 a.m. Tuesday. Department of Corrections spokesman John Schadl says the lockdown involved all 10 state prisons.

U.S. Attorney spokeswoman Jeanne Cooney tells the Star Tribune (http://bit.ly/xIQSQC ) the lockdown was needed “for safety’s sake,” but she did not explain further.