WASHINGTON — The Obama administration escalated its crackdown on health-care fraud Wednesday, announcing charges against 91 people in eight cities who are accused of bilking the Medicare system out of nearly $300 million and victimizing the elderly and disabled people who rely on the federal insurance program.

Among those charged in the coordinated series of arrests was a doctor in Detroit who allegedly billed Medicare for services provided to dead people and claimed that he performed psychotherapy treatments more than 24 hours a day. Other doctors, nurses and health-care company owners were charged in various schemes to get paid for services that were medically unnecessary or never provided.

“From Brooklyn to Miami to Los Angeles, the defendants allegedly treated the Medicare program like a personal piggy bank,” Lanny Breuer, assistant attorney general for the Justice Department’s criminal division, said at a news conference.

It was unclear whether lawyers had been appointed for the defendants, 70 of whom were charged in indictments unsealed this week. The other 21 were charged in recent weeks. More than 55 defendants had been arrested by Wednesday afternoon, in addition to others who turned themselves in to authorities.

The arrests, announced by Attorney General Eric Holder and Health and Human Services Secretary Kathleen Sebelius, marked the latest step in a campaign against fraud that the administration calls a key part of its health-care reform agenda.