A U.S. House of Representatives inquiry into allegations that senior executives at the Veterans Affairs Department abused their positions of authority hampers ongoing investigations, agency officials said.

Deputy VA Secretary Sloan Gibson made the warning in a letter Tuesday to House Veterans Affairs Committee Rep. Jeff Miller, R-Florida, explaining why he would not allow five VA executives to testify before the House panel on Wednesday on allegations raised in a report by the department's office of the inspector general.

"[This] committee's questioning VA witnesses about the individual accountability issues raised in the OIG report creates the appearance that accountability actions may have been pre-decided," Gibson wrote. "The OIG report ... is not evidence, but simply the investigator's summary of what they believed the evidence to show."

In addition to the VA's investigation, the U.S. Attorney's office is also reviewing the IG report to determine if criminal charges should be brought against anyone.

Gibson said that while the IG report came out last month, he only received on Oct. 16 the "full evidentiary record" upon which investigators drew their conclusions.

"It is critical that I be afforded the opportunity to review the evidence and make the necessary decisions independent of undue external influence," he wrote. "I ask, simply, that the Committee wait until the appropriate time to question witnesses about these still-pending matters."

But the House committee on Wednesday voted to subpoena the five witnesses, including former Under Secretary for Benefits Allison Hickey, who resigned from her position last week. The five must now appear before the panel on Nov. 2.

During the hearing, Miller said Gibson informed the committee last week that none of the witnesses the panel asked to hear from would attend, but that he would testify on behalf of the VA. Miller rejected Gibson's bid to testify.

In addition to Hickey, the lawmakers have subpoenaed Diana Rubens, director of the VA's Philadelphia Regional Office; Kimberley Graves, director of the St. Paul, Minnesota, Regional Office; Antoine Waller, director of the Baltimore Regional Office; and Robert McKenrick, director of the Los Angeles Regional Office.

According to the IG report, Rubens had been a deputy under secretary for field operations until she took over as director for Philadelphia post in June 2014, replacing McKenrick. McKenrick told the IG he was told to take the Los Angeles position or lose his job.

Graves, formerly director of the Veterans Benefits Administration's Eastern Area Office (now called the North Atlantic District) took over as director of the St. Paul position in October 2014. Waller, who had held that position, told investigators he reluctantly left it for the Baltimore position after Graves' subordinate told him his name had already been given to VA Secretary Bob McDonald for the job and he was expected to take it.

In addition to getting jobs the IG claims they pushed others out of, Rubens and Graves also got hundreds of thousands of dollars through a moving assistance program. Rubens got $274,000 in moving assistance and Graves $129,000.

Rubens' windfall came in the form the Appraised Value Offer program, which pays an employee for the value of their home as an incentive for a job move.

Gibson said in his letter that VA, "a result of recent report findings, effective October 1, 2015 ... ceased offering the Appraised Value Offer (AVO) program to its employees."

Gibson also countered a comment Miller made in an Oct. 16 letter to VA, when the lawmaker said that neither he, "nor any Member of this Committee, exerted any pressure on the Department regarding [accountability] decisions" in this case.

"This ... simply does not match up with the facts," Gibson said. "The record reflects that you, the Committee, and other members of Congress have already exhorted [VA Secretary Bob McDonald] to fire several named VA employees."

Gibson quoted Miller as saying on Sept. 28 that he encouraged McDonald "to utilize every tool available to him to ensure that these VA managers and leaders [Rubens and Graves] are immediately held accountable for their actions."

Gibson next quoted from Miller's Oct. 16 public statement on Hickey's resignation, in which the lawmaker said Hickey "leaves the Department amid a damning [OIG] report linking her to a scheme in which senior Veterans Benefits Administration officials abused their authority, resulting in the misuse of hundreds of thousands of taxpayer dollars."

The deputy secretary told Miller that he and other committee members have made similar statements in the past when critical IG reports have been published.

"While [lawmakers] may not intend to advocate for a particular accountability decision, these statements clearly create the appearance of Congressional pressure for the Department to discipline particular employees in this matter," he said.

Rep. Corrine Brown, D-Florida, the ranking Democrat on the committee, said she is concerned about the IG claims and conclusions but also wants everything handled properly.

"VA employees need to have a process that is fair," she said. "I understand the serious nature of this ... I'm not urging a certain action, but that a suitable action be taken at the appropriate time."

--Bryant Jordan can be reached at bryant.jordan@military.com. Follow him on Twitter at @bryantjordan.