A nonprofit provider of mental health services paid nearly $557,000 to settle allegations of improper billing to government health programs, the state attorney general's office said yesterday.

Tri-City Mental Health Center began reviewing employee complaints about irregularities in its government claims practices in 2003, and the nonprofit's board ordered an outside audit, Massachusetts Attorney General Martha Coakley said.

Tri-City reported the improper billing to the government in late 2004, and was never charged.

State and federal investigators found Tri-City Mental Health billed the state Medicaid program and the state Department of Mental Health for psychiatric services that were never provided or couldn't be documented.

The improper billing occurred for more than two years, starting in Sept. 2001 at a center in Malden.

At least one manager at the Malden office was fired as a result of Tri-City's internal investigation, Coakley said.

Ellen Dalton, a manager at Tri-City, said the improperly received government payments were used to fund the nonprofit's operations, not for any personal use by its nearly 500 employees.

Dalton said Tri-City set aside cash from recent years' operations, and has paid the $556,687 settlement total in full.

"The agency is ready to move forward, and no services will be disrupted," she said.

The nonprofit, which began operations in the 1960s, runs mental health centers in the neighboring communities of Malden, Medford, and Everett.

The settlement total equals the amount of money that investigators found had been improperly billed, plus interest, according to Dalton.

Under the settlement, Tri-City agreed to ensure future compliance with rules governing Medicare reimbursement.

The settlement relieves Tri-City and its board of any civil or administrative liability.

Coakley said Tri-City "has cooperated fully with the investigation."