The head of the agency that provides health care to military veterans was due at the White House on Friday to learn if a scandal over delayed treatment will cost him his job.
President Barack Obama is under pressure to fire Eric Shinseki after Veterans Administration staff falsified waiting lists, holding up care for hundreds of former service members.
Before his meeting, addressing a conference on care for homeless veterans, Shinseki took responsibility for the situation and said he had begun moves to clean house at his agency.
"After Wednesday's release of an interim inspector general report, we now know that VA has a systemic, totally unacceptable lack of integrity within some of our veterans' health facilities," he admitted.
The former general said that when he first became aware of the problems with the waiting lists he had thought they were isolated cases, but that he had now discovered widespread failings.
"I can't explain the lack of integrity amongst some of the leaders of our health care facilities," he said.
"This is something I rarely encountered during 38 years in uniform. And so I will not defend it because it is indefensible. But I can take responsibility for it. And I do."
Shinseki apologized to all veterans who had been denied care and said he had begun procedures to sack managers at the agency's office in Phoenix, Arizona, where the scandal first came to light.
He also said that no VA executives would receive performance bonuses this year.
But it was not clear if the action, taken after a damning report from the agency's inspector general and amid furious criticism from the media and lawmakers, would be enough to save his job.
On ABC television Obama called Shinseki "an American hero, a wounded vet, somebody who led our troops during difficult times," but stopped short of saying whether he would stay in the post.
"He's going to report back to me on what he's seen and I'll have a serious conversation with him about whether he thinks that he is prepared and has the capacity to take on the job of fixing it," he said.
The inspector general found that 1,700 veterans in the Phoenix area alone had been kept off the main waiting list for primary care. Up to 40 patients are said to have died while waiting for treatment.