United Medical Center, formerly the Greater Southeast Hospital, recently received a $11 million cash infusion to help cover unpaid bills. (Sarah L. Voisin/The Washington Post)

An employee at the city-owned United Medical Center is said to have received several hundred thousand dollars in improper payments, the hospital’s board said Thursday.

The salaried employee, who was not named, “inappropriately manipulated the IT/payroll system to be paid overtime hours” even though the person was not eligible to be paid overtime, according to a hospital statement.

An official in Mayor Vincent C. Gray’s administration, who was not authorized to speak publicly on the matter, said the improper overtime payments are in the range of $400,000, with additional bonus payments in the six-figure range also at issue. The manipulation, the official said, dated back to before the city assumed control of the hospital in 2010.

Hospital spokeswoman Natalie Williams said the employee was fired after the manipulation was discovered. “We have taken all necessary measures to increase controls to further halt manipulation of the systems,” she said in a statement.

The matter has been referred to Inspector General Charles Willoughby and Attorney General Irvin B. Nathan for investigation, Williams said.

Management of United Medical Center was recently assumed by Huron Consulting, which was hired by the city on a two-year, $12.4 million contract to overhaul its operations.

The hospital has long been on shaky financial footing. In the 2012 fiscal year, it recorded a $322,000 loss after the District infused $7.7 million in cash and forgave a $6 million loan. Last month, the city gave the hospital an additional $11 million cash infusion to help cover unpaid bills.