All of Florida's 97,000 state prison inmates are on lockdown — and will remain confined to their dorms at least through the weekend — in response to unspecified threats about possible uprisings, officials from the Florida Department of Corrections confirmed Thursday.

The unprecedented step comes one day after the agency announced it had canceled weekend visitation at all of its 50 major institutions, as well as annexes, work camps and re-entry centers. There was no indication Wednesday that any other restrictions had been instituted. In fact, a spokeswoman said that no other "basic privileges'' would be affected.

However, on Thursday, the Miami Herald learned that state prisons were on a systemwide lockdown — and that all educational, vocational, rehabilitation, ministry and recreation programs have been scrubbed until further notice. Inmates are confined to their dorms, except at mealtime, FDC officials confirmed.

The agency has not said specifically what led to the lockdown, other than that the department had received "credible intelligence'' that "small groups'' of inmates were planning to cause disturbances.

"Everything we are doing is based on the safety of the institutions, the staff and the inmates,'' said Michelle Glady, FDC spokeswoman.

Social media has been advertising a "Millions for Prisoners' Human Rights" rally on Saturday in Washington, but it's not clear who is spearheading the movement. Postings advertise the effort as a way to raise awareness about mass incarceration and human rights violations in prisons across the country.

Glady said the department's intelligence division has received information that the disturbances could be timed to coincide with the march.

Florida inmates, their families and civil rights groups have long protested the state's prison conditions. Over the past year, state Rep. David Richardson, a Miami Beach Democrat, has made unannounced visits to Florida prisons and found inmates — especially in the restrictive status known as confinement — without basic necessities, such as toilet paper, toothbrushes, toothpaste, pillows, sheets, shirts and soap.

Richardson said Thursday that he had been briefed on the current prison security precautions, but he would not say whether officials told him that all the prisons were on lockdown.

Violence among inmates — especially those in gangs — is at an all-time high. Corrections officers have been stabbed and beaten, and prisoners have been killed in clashes over the past year.

Staffing is stretched so thin that limits have already been placed on educational and vocational programming at many prisons.

Florida has the nation's third-largest prison system, behind California and Texas. The FDC has 148 facilities statewide, including 50 major institutions, 17 annexes, seven private facilities, 35 work camps, three re-entry centers, two road prisons, one forestry camp and one boot camp. It has a budget of $2.4 billion, and more staff than any other state agency.

To retain and recruit more officers, state lawmakers recently approved the first raise in years and the agency is offering signing bonuses for new officers at institutions with serious staff shortages.

Last year, there were violent outbursts at several Panhandle prisons in advance of a nationwide prison strike scheduled on Sept. 9 — the 45th anniversary of the deadly riot at Attica prison in New York.

There were no serious injuries last year, but three prisons were locked down. One rebellion, at Holmes Correctional Institution, involved more than 400 inmates and caused damage to nearly every dorm.

Glady said some of the prisons in the state's Panhandle have been gearing up for the possibility of violence, which is one reason they've been put on lockdown. She said most prisoners are allowed to make phone calls — and all of them are permitted to shower and go to chow hall. Only Franklin Correctional Institution, in Franklin County, is on full lockdown, where inmates are not receiving any privileges. She said that's because of a more serious security concern, which she would not detail.