WASHINGTON (Reuters) - The U.S. Environmental Protection Agency’s watchdog is expanding a review of administrator Scott Pruitt’s frequent travels to his home state Oklahoma to include more recent trips taken on military and charter flights, according to a memo seen on Friday.

FILE PHOTO - Scott Pruitt, Administrator of the U.S. Environmental Protection Agency, answers a question during the Concordia Summit in Manhattan, New York, U.S., September 19, 2017. REUTERS/Jeenah Moon

The Office of Inspector General had been investigating the “frequency, cost and extent” of Pruitt’s travels to Oklahoma through July 31, and will now expand the “active audit” to include all travel, including the use of private and military flights he has taken up to Sept. 30.

The expanded review coincides with heightened scrutiny surrounding the travels of President Donald Trump’s cabinet officials with reports that some have spent tens and hundreds of thousands of dollars for non-commercial flights.

Health and Human Services Secretary Tom Price resigned last week over his use of costly private charter planes for government business.

The Interior Department’s own inspector general last week confirmed it also opened an investigation into travels by Interior Secretary Ryan Zinke after receiving numerous complaints about his use of three chartered flights, including one on an aircraft owned by an oil and gas executive.

Energy Secretary Rick Perry also used a private charter flight last week, Reuters reported. The flight cost $11,000, according to travel records provided to Reuters by the Department of Energy.

The records show that Perry took four non-commercial flights between May and last week totaling nearly $56,000 of taxpayer money.

Department spokeswoman Shaylyn Hayes said in a statement on Friday that in the “rare instances where government-owned or chartered aircraft have been used, trips were pre-approved by an Ethics officer within the Office of General Counsel.”

Separately, a spokeswoman for the Energy Department’s inspector general office could not confirm nor deny whether it is investigating his travels.

In addition to investigating the frequency of Pruitt’s travels, the watchdog is also evaluating whether Pruitt followed EPA travel protocols and whether “EPA’s policies and procedures are sufficiently designed to prevent fraud, waste and abuse with the Administrator’s travel.”

Pruitt has taken at least four flights that were either not commercial or military-chartered since mid-February, according to government records. EPA spokeswoman Liz Bowman said the four non-commercial flights had been cleared by EPA lawyers.

Pruitt had also traveled to Oklahoma on at least 43 of the 92 days of March, April and May, according to copies of his travel records obtained by the Environmental Integrity Project watchdog and reviewed by Reuters last month, which prompted the initial investigation.