TULSA (AP) — The state has joined federal prosecutors in alleging that Oklahoma-based Emergency Medical Services Authority and its director were part of a kickback scheme that involved the state's former ambulance services provider.

The Oklahoma Attorney General's Office filed a complaint in a Texas federal court this week asking to partially intervene in a whistleblower lawsuit against EMSA, a public trust that serves more than 1.1 million residents, including those in Tulsa and Oklahoma City.

The state's complaint alleges that the Oklahoma Health Care Authority paid more than $64 million to EMSA "for false Medicaid claims submitted for services provided by Paramedics Plus," a Texas-based ambulance provider that contracted with EMSA, the Tulsa World reported.

Investigators allege the kickbacks and bribes happened between 2008 and 2013, when Paramedics Plus contracted with EMSA for ambulance service in Oklahoma. They ranged from cash payments to Williamson to political contributions, according to the complaints.

EMSA has denied the allegations, and Paramedics Plus officials said its payments to EMSA were considered part of a "profit cap."

The whistleblower lawsuit was initially filed by a former employee of Paramedics Plus, and federal prosecutors in Texas stepped in after investigating. EMSA and its president, Stephen Williamson, are named as defendants in the federal and state complaints.

The Oklahoma complaint cites the Oklahoma Medicaid False Claims Act, the Oklahoma Medicaid Integrity Act and common law to recover "millions of dollars in damages and civil penalties from defendants for knowingly submitting, or causing to be submitted, false claims" to Oklahoma's Medicaid, SoonerCare.

EMSA officials have continued to stand by Williamson and its own actions.

"EMSA's Board of Trustees is diligently working with legal counsel and experts in the field, and we believe that the law and facts are on our side," board Chairwoman Allison Petersen said.