Story highlights U.S. Secretary of Veterans Affairs Eric Shinseki calls for a review

Shinseki announced that the Phoenix VA director has been placed on leave

CNN has been investigating allegations of a secret wait list at Phoenix VA

In CNN interview, Director Sharon Helman denied existence of such a list

The director of the Phoenix Veterans Affairs Health Care system and two others have been placed on administrative leave amid claims of a secret waiting list and claims that 40-plus veterans died waiting for care.

These allegations have been exposed in a series of exclusive reports by the CNN Investigations unit.

The announcement Thursday by U.S. Secretary of Veterans Affairs Eric Shinseki came a day after officials at the Phoenix VA denied in interviews with CNN the existence of such a list, only to be called liars hours later by the top VA physician who first appeared on CNN and brought the allegations to light.

"We believe it is important to allow an independent, objective review to proceed," Shinseki said in a written statement. "... These allegations, if true, are absolutely unacceptable and if the Inspector General's investigation substantiates these claims, swift and appropriate action will be taken."

Those placed on leave, according to the statement, are Phoenix VA Director Sharon Helman, Associate Director Lance Robinson and a third employee, who was not identified by name.

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Shinseki's office denied repeated requests by CNN over six months to interview the secretary about the allegations.

Sources told CNN the managers at the VA concocted an elaborate scheme to cover up long wait times there. The sources said more than 1,400 veterans were placed on the purported secret list and that documents were shredded to hide the evidence. According to sources, at least 40 U.S veterans died waiting for care at the facility, many of whom were on the list.

These issues raised in CNN's exclusive investigation have quickly drawn attention in Washington.

On Monday, President Barack Obama said he called on Shineski to investigate what has happened in Phoenix.

In recent days, numerous members of Congress have called for hearings on the Phoenix VA, and at least three members of Congress have publicly called for Helman's resignation.

But in an interview with CNN on Tuesday, Helman and her chief of staff, Dr. Darren Deering, denied any secret effort to cover up or hide wait times.

"We have never instructed our staff to create a secret list, to maintain a secret list, to shred a secret list -- that has never come from our office as far as instruction to our staff," said Deering.

"It's never come from me," added Helman.

Dr. Sam Foote, a 24-year VA physician and clinic director, recently retired and went public with the details of the list, went on the air publicly for the first time with CNN one week ago.

He denounced Helman's claim.

"They started this secret list in February of 2013," Foote said. "At some time, they changed over from paper to electronic, in early summer, maybe approximately June or July. And transferred names over to the electronic waiting list. And she [Helman] was called on an ethics consult evaluation about that -- it's written down, documented in July."

That documentation includes e-mails from July 2013, which were reported by CNN, that show top management, including Helman, were well-aware about the actual wait times, knew about the off-the-books list and even defended its use to her staff.

When directly asked earlier this week about whether evidence of wait times was shredded and whether the secret list existed, Deering stated:

"I think there is some confusion amongst our staff. When we came on as a leadership team in 2012, the practice at that time was that they would schedule new veterans who would were coming in for care way out into the future. Sometimes a year, sometimes 14 months. And that was the appointment that that veteran was given.

"As we started to tackle our challenges of access, we implemented a tool that the VA uses nationally called the electronic wait list. And what that tool is it's an electronic waiting list that allows us to everyday look to see who is waiting for an appointment.

"So what we did is we took those patients that were scheduled way out into the future, and we put them on this national tool that the VA uses so that we could track them. What that did is, rather than having an appointment 14 months out into the future, it put them on this EWL electronic waiting list, so that when we had an appointment that came open, so if a veteran called next week and canceled their appointment, we could pull a veteran off this list and get them into that slot.

"So it actually improved the probability of these veterans getting an appointment sooner. And in that transition time, I think there was some confusion among staff, I think there were some folks who did not understand that, and I think that's where these allegations are coming from."