In the largest ever crackdown on health-care fraud by the Justice Department, criminal charges have been filed against 243 people across the nation involving $712 million in false billing from Medicare, officials announced Thursday. Among those charged over the past several days are 46 doctors, nurses and other medical professionals as well as others accused of health-care fraud, violations of anti-kickback statutes, money laundering and identity theft. The cases, which span 17 federal judicial districts, are not all related to each other. But they all involve alleged fraud on Medicare, the federal program that provides health-care benefits to primarily senior citizens, as well as on Medicaid, the government health program for the poor.

Attorney General Loretta Lynch. Getty Images

"This action represents the largest criminal health-care fraud takedown in the history of the Department of Justice," said Attorney General Loretta Lynch, as she announced the sweep by the Medicare Fraud Strike Force. "The defendants include doctors, patient recruiters, home health-care providers, pharmacy owners and others," Lynch said. "They billed for equipment that wasn't provided, for care that wasn't needed and services that weren't rendered." Read More$3,300 higher Obamacare bills possible

More than 40 of the defendants were charged with false billing related to Medicare Part D, the prescription drug component of the program, and the fastest-growing part of that health coverage system. Lynch said those cases are the first large-scale effort to combat Medicare Part D fraud. FBI Director James Comey said that all of the defendants charged in the sweep "targeted the system each of us depends on in our most vulnerable moments." "Health-care fraud is a crime that hurts all of us, and each dollar taken from programs that help the sick and the suffering is one too many."

Lynch said that "one of the more egregious allegations" involved owners of a Miami health facility who "billed for intensive psychotherapy sessions that resulted in tens of millions of dollars in reimbursement for the doctors based on treatment that was nothing more than moving patients to different locations." Read MoreYour drug prices too high? Here's who many blame

"Several of these patients suffer from illnesses like Alzheimer's and dementia and were unable to even communicate with their supposed caregivers or therapists," she said.

In another case in southern Florida, the owner of a health-care provider "received $1.6 million for Medicare Part D prescription drugs the provider never purchased and certainly never dispensed," Lynch said. And in a third case, she said, a doctor in eastern Michigan "is alleged to have prescribed unnecessary narcotic pain medications to patients in exchange for the use of their identification information to generate false billings." Read MoreBig Obamacare funds 'at risk': Audit

When some of the patients tried to withdraw from the scheme, the doctor allegedly used their addiction to keep patients bound to it, Lynch said.