United Medical Center, the controversial and long-troubled hospital owned by the District government, said on Thursday that it has fired an employee for allegedly embezzling at least $400,000.

"A salaried employee of UMC inappropriately manipulated the IT/payroll system to be paid overtime hours," the hospital said in a written statement. "Under federal law, salaried employees are exempt from overtime."

A District government official, who requested anonymity to discuss the ongoing investigation, said that the theft was "well in excess of $400,000 and could be as high as double that."

The hospital described the unidentified worker as "a longtime employee" and said that the alleged fraud had transpired over several years.

"News of this inappropriate activity comes as a complete shock to the board of directors and hospital management," said Natalie Williams, a hospital spokeswoman. "We are fully cooperating with law enforcement in their efforts. Additionally, we are working with our insurance carries to ensure repayment and recovery of funds."

The hospital, which the city seized control of in 2010, said the city's inspector general and attorney general are investigating.