WASHINGTON (AP) — President Barack Obama is dispatching one of his closest White House advisers to oversee a review of the beleaguered Veterans Affairs Department as the agency grapples with allegations of treatment delays and preventable deaths at a Phoenix veterans hospital.

White House deputy chief of staff Rob Nabors will be temporarily assigned to the VA to work on a review focused on policies for patient safety rules and the scheduling of patient appointments, officials said Wednesday. The move signals Obama's growing concern over problems at the department, particularly recent reports that hospital administrators in Phoenix kept an off-the-books list to conceal long wait times as 40 veterans died waiting to get an appointment. Similar problems have since been reported in other states.

The allegations have sparked a firestorm inside the VA and on Capitol Hill. The American Legion and some congressional Republicans have called for the resignation of Veterans Affairs Secretary Eric Shinseki, who is scheduled to testify before a Senate committee Thursday.

"While we get to the bottom of what happened in Phoenix, it's clear the VA needs to do more to ensure quality care for our veterans," Obama said in a statement. "I'm grateful that Rob, one of my most trusted advisers, has agreed to work with Secretary Shinseki to help the team at this important moment."

Obama ordered the patient policy review after the Phoenix allegations became public. But officials said Shinseki requested more help with the review, leading Obama's chief of staff, Denis McDonough, to tap Nabors for the assignment.

The move is similar to the action the White House took last year when it assigned longtime Obama aide Jeffrey Zients to take over management of the troubled HealthCare.gov website from officials at the Health and Human Services Department. HHS Secretary Kathleen Sebelius later resigned her post.

"We are glad the president took this first step to ensure the White House is involved in solving this crisis at the VA," said Tom Tarantino, the chief policy officer of Iraq and Afghanistan Veterans of America. "We need bold reform to establish a culture of accountability throughout the VA system and hope that Mr. Nabors' presence will help ensure that this type of failure never happens again."

Despite calls for Shinseki to step down, the White House insists that Obama continues to have confidence in the secretary, a retired four-star Army general. Shinseki said he welcomed Nabors' help in ensuring veterans have access to timely, quality health care.

"If allegations about manipulation of appointment scheduling are true, they are completely unacceptable — to veterans, to me and to our dedicated VA employees," Shinseki said.

Though Nabors has kept a low public profile, he is one of Obama's closest advisers and has played key roles in the president's fiscal battles with congressional Republicans. Nabors, the son of an Army veteran, was appointed deputy chief of staff following Obama's re-election and previously served as the president's chief congressional liaison and deputy budget director.

The VA operates the largest integrated health care system in the country, with more than 300,000 fulltime employees and nearly 9 million veterans enrolled for care. But the agency has struggled with the influx of new veterans entering the VA system as the wars in Iraq and Afghanistan come to a close.

The allegations against the Phoenix hospital have been particularly troubling. Former hospital employees contend that up to 40 patients died while waiting to see a doctor and that the hospital kept a secret list of patients waiting for appointments to hide the treatment delays.

VA facilities in South Carolina, Florida, Pennsylvania, Georgia and Washington state have also been linked to delays in patient care or poor oversight. An internal probe of a Colorado clinic found that staff had been instructed to falsify records to cover up delayed care at a Fort Collins facility.

The VA has acknowledged that 23 patients have died because of problems related to care since 1999, according to an ongoing nationwide internal VA review, which showed that delays often occur when a doctor refers a patient to another physician, such as a specialist. During the same time period of the deaths, more than 250 million of these consults were requested.

The review Nabors will oversee is separate from an inspector general's investigation into the Phoenix allegations that is already underway. Three executives at the hospital have been placed on leave while the allegations are being investigated.

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