 -- The inspector general's office at the U.S. Department of Health and Human Services confirmed Friday it is investigating the private jet travel of the agency's chief, Tom Price, who reportedly chartered five flights last week, drawing widespread criticism from congressional Democrats.

Price's travel, first reported by Politico on Wednesday, comprised trips to Maine, New Hampshire and Pennsylvania aboard private planes estimated to cost tens of thousands of dollars per flight. Politico noted that the chartered jets did not explicitly violate government regulations, but that past health secretaries have typically flown commercially, especially when traveling domestically.

The news outlet followed up with an additional story Thursday that reported Price flew on a total of 24 private flights since early May.

“[The Office of Inspector General] is conducting a review of Secretary Price’s federal travel using chartered aircraft. The review focuses on whether the travel complied with Federal Travel Regulations, but may encompass other issues related to the travel," read a statement Friday from Tesia Williams, a spokesperson for HHS Inspector General Daniel Levinson. "We take this matter very seriously, and when questions arose about potentially inappropriate travel, we immediately began assessing the issue."

Williams further told ABC News that the inspector general has not limited the scope of the investigation to what has already been reported.

"If anything else comes up, we will take a look and dig into those items," she said.

Democratic ranking members of five congressional committees sent a letter to Levinson on Thursday to request a review of Price's observance of departmental rules.

The letter cited the Code of Federal Regulations which notes, "...because the taxpayers should pay no more than necessary for your transportation, generally you may travel on Government aircraft only when a Government aircraft is the most cost-effective mode of travel."

At least two Democratic members of Congress seized on the report to promote rail travel, their preferred method of commuting to Washington, D.C., while criticizing Price.

"Mr. Secretary, I invite you to join me on [Amtrak] when you travel to Philly," tweeted Sen. Tom Carper, D-Del. Wednesday. "I assure you it's very comfortable with shorter security lines."

"Dear Tom Price, As someone who travels from DC to Philly every week let me recommend Amtrak," tweeted Rep. Brendan Boyle, D-Pa., whose district encompasses a portion of the Pennsylvania city.

The Department of Health and Human Services defended Price's travel choices by noting the secretary's "demanding schedule" and the size of the "$1.2 trillion agency."

"The travel department continues to check every possible source for travel needs including commercial, but commercial travel is not always feasible," read a statement from Charmaine Yoest, the assistant secretary for public affairs at the agency. "The President has made it clear his Administration will move power out of Washington and return it to the American people. Secretary Price will continue meeting with the American people outside of the Beltway to hear their concerns and ensure HHS makes decisions that best provide for their needs.”

Since his appointment as health secretary and during his tenure in the House of Representatives -- part of which was spent as chair of the House Budget Committee -- Price has frequently criticized government waste.

Speaking before Congress in March about his department's budget, Price said, "One of our priorities is to try to find the waste and abuse that exists," in regard to government outlays on Medicare.

Price publicly decried federal spending and attacked "fiscal irresponsibility" in a 2009 CNBC interview amid a ultimately-abandoned proposal to spend $550 million on planes for members of Congress and government officials.

The issue of Price's travel follows an ABC News report last week that Treasury Secretary Steve Mnuchin faced an inquiry by the Treasury Department's inspector general over a request to use a government airplane to travel to his European honeymoon this summer. The inquiry is the second travel-related review faced by Mnuchin. His official trip to Kentucky during August's solar eclipse is also being reviewed.

Mnuchin dropped the honeymoon travel request but later defended it as in the interest of "national security" so he would have a secure line of communication.