(Cliff Owen/AP Photo)

Eric Shinseki made no mention of resigning today when he addressed a homeless veterans advocacy group, but he apologized for the scandal over veterans' wait times for health care and said he was surprised by the "lack of integrity" some VA officials had displayed, announcing a series of actions he's taken since the release of Wednesday's interim findings by the Veterans Affairs Administration's inspector-general investigation.

"I apologize as the senior leader of the Department of Veterans Affairs," Shinseki said.

"I can't explain the lack of integrity among the leaders of some of our health care facilities," Shinseki told the group, calling it something he "rarely encountered" during his time in uniform.

Shinseki has come under fire over veterans' wait times for doctors' appointments at a VA hospital in Phoenix and others across the country.

READ: Veterans Affairs Scandal: What You Need To Know

Shinseki said he initially had placed his trust in faulty accounts by VA officials of how wait lists were handled, leading him to believe that the problem of veterans not being placed on official wait lists was an isolated one, not systemic across the VA. After the preliminary IG findings released this week, Shinseki now considers the problem of how wait times are handled to be "systemic" in the VA.

"I was too trusting of some," Shinseki said, apologizing to veterans' organizations and lawmakers who supported him, also saying that "leadership and integrity problems can and must be fixed - and now."

Shinseki spoke to the National Coalition for Homeless Veterans, speaking for the fifth time at the group's annual conference at the Grand Hyatt in downtown Washington, D.C.

He also told the group that the VA will "use all authority at our disposal and enforce accountability" for those responsible for mishandled wait times, adding that he's initiated the process of firing senior VA leaders in Phoenix.

After veterans were kept off official wait lists, Shinseki said he's directed the VA to stop using veterans' wait times to evaluate VA employees. Presumably, that would remove an incentive for employees to keep veterans off official wait lists and artificially reduce the time veterans are known to be waiting to receive doctors' appointments. He added that no VA senior executive will receive a performance award this year and asked Congress to support a bill by Sen. Bernie Sanders, I-Vermont, to give him more authority to remove senior VA officials.

Shinseki arrived to a standing ovation and praise from the National Coalition for Homeless Veterans' chairman for Veterans Affairs Administration initiatives under Shinseki's watch to decrease veteran homelessness from 75,000 in 2009 to less than 58,000 today, according to the group. Shinseki has made veteran homelessness a priority during his tenure. The group applauded him warmly as he touted accomplishments in reducing veteran homelessness and as he announced the actions he's taken after the VA scandal.

A cascade of lawmakers - Republicans and Democrats alike - have called on Shinseki to resign in the wake of the ongoing scandal.

READ: More Than 125 Members of Congress Want Shinseki Gone

The preliminary findings of a Veterans Affairs inspector general report this week validated allegations that the queue system for veterans seeking doctors' appointments had been mishandled in Phoenix, putting some 1,700 vets at risk of being lost in the system because they were not added to official wait lists.

Shinseki called the preliminary findings "reprehensible" on Wednesday, announcing he had ordered all of those 1,700 vets to be triaged immediately.

While more than 100 lawmakers have called on him to resign, House Speaker John Boehner, R-Ohio, and Minority Leader Nancy Pelosi, D-California, have publicly reserved judgment.

President Obama told ABC News he will have a tough conversation with Shinseki about whether he can fix the problem and whether he should remain on the job, as Jonathan Karl reported on "GMA."

Shinseki held a closed-door meeting with veteran service organizations and VA officials on Wednesday after the report's release.

NCHV, the group that hosted Shinseki on Friday, was not present at that meeting but supports Shinseki and says he should not resign.

"No man or woman has done more to end the blight on this nation that is veteran homelessness than Secretary Shinseki," the group said in a written statement to media. "For more than 20 years, NCHV has advocated for the federal resources to house and support homeless veterans. Not until Secretary Shinseki took leadership of the VA were these cries for help for those too often overlooked finally heard."