WASHINGTON — A top Veterans Affairs Department official is acknowledging “an integrity issue here among some of our leaders” as the embattled agency reels from mounting evidence that workers fabricated data on veterans’ waits for medical appointments in an effort to mask frequent, long delays.

“It is irresponsible,” Philip Matkovsky, a top VA official who helps oversee its administrative operations, told the House Veterans Affairs Committee at an unusual Monday evening hearing. “It is indefensible, and it is unacceptable. I apologize to our veterans, their families and their loved ones.”

Matkovsky did not specify which VA officials had questionable integrity. The agency has started removing top officials at its medical facility in Phoenix.

a focal point of the department’s problems, and investigators have found indications of long waits and falsified records of patients’ appointments at hundreds of facilities.