HARRISBURG — The University of Pittsburgh Medical Center and Highmark Inc. have agreed to an 18-month extension on a regional health care contract that will keep the medical center’s hospitals and doctors in Highmark’s network through the end of 2014, Gov. Tom Corbett said Wednesday.

The agreement was reached Tuesday evening, a Corbett aide said, although the governor said he did not have complete details, and a Highmark spokesman declined to give additional details beyond a joint statement the groups issued through Corbett’s office.

The governor said he hadn’t sat at the negotiating table, but had applied pressure to resolve a dispute that was creating uncertainty for about 2.5 million Highmark insurance customers in Western Pennsylvania.

“I encouraged them that they need to address this issue, they need to get it done,” Corbett told a Capitol news conference. “With the assistance of the Legislature backing me up, (I told them) that if they did not get this done, we would get it done for them and I don’t think anybody wants to see government get into what is really a business relationship and I think they took that to heart and were able to resolve this.”

As part of the deal, Highmark agreed to stop pressing for legislation to force the two into binding arbitration. Highmark has said UPMC was seeking a 40 percent increase in reimbursement payments.

On Wednesday, Highmark spokesman Michael Weinstein would not say whether higher reimbursements are part of the pact. But a person familiar with the agreement said that, as part of it, Highmark will pay higher reimbursement rates similar to those paid by commercial insurers Aetna, Cigna and United.

Corbett said he had asked David Simon, executive vice president of Jefferson Health System in the Philadelphia area, to help mediate.

The dispute over in-network coverage disrupted negotiations last June when Highmark, Pennsylvania’s largest health insurer, announced a $475 million takeover of the financially troubled six-hospital West Penn Allegheny Health System.

UPMC had said that made Highmark a direct competitor to its system of about 20 hospitals and 3,000 physicians. Under pressure from state lawmakers and the Corbett administration, the groups in December had agreed to a one-year contract extension that expires June 30, 2013.