The top security official for embattled Environmental Protection Agency head Scott Pruitt abruptly left office ahead of his scheduled questioning before a congressional panel, one of two top aides whose departures were announced Tuesday amid a series of federal ethics investigations of the agency.

In statements, Pruitt gave no immediate reasons why the two men — security chief Pasquale "Nino" Perrotta and Albert Kelly, a former Oklahoma banker who ran the EPA's Superfund program — were leaving.

Perrotta is due to appear Wednesday for a transcribed interview by staffers of the House Oversight Committee. Committee aides said his resignation was not expected to affect his appearance.

Pruitt's spending on security, and some of EPA's security contracts with Perrotta, are among the topics of more than a dozen federal probes involving the EPA under Pruitt, a former Oklahoma attorney general.

Pruitt said Perrotta was retiring, and praised him for hard work and dedication.

Pruitt thanked Kelly for what he said was his "tremendous impact" in Kelly's year overseeing the nation's Superfund program, charged with handling the cleanup of toxic waste sites.

Pruitt hired Kelly, an Oklahoma banker, at EPA after federal banking regulators banned the man from banking for life. Regulators have not publicly specified the actions that led to the banking ban. Days ago, Rep. Scott Peters, D-Calif., pressed Pruitt for more details about why exactly Kelly had been sanctioned by regulators.

"I think Mr. Kelly, if he's willing to share that with you, he should do that," Pruitt said Thursday.

EPA spokespeople Jahan Wilcox and Liz Bowman did not immediately respond to a question asking whether the two departures were related to ongoing federal investigations.

Democrats in Congress asked for federal investigations of Kelly's reported loans to Pruitt himself while the two were still in Oklahoma. Kelly is not among the other EPA officials whom the House Oversight Committee members had summoned for questioning.

Pruitt weathered six hours of grilling from congressional Democrats last week over the steady flow of news reports and announcements of new investigations involving alleged ethical lapses at his agency, including spending for Pruitt on round-the-clock security guards, first-class plane tickets, and a $43,000 soundproof telephone booth.

Pruitt repeatedly deflected blame, saying subordinates had taken the questioned actions without his knowledge.

He pledged then to change course at the agency on the questioned spending and other issues. "Ultimately, as the administrator of the EPA, the responsibility of identifying and making necessary changes rests with me and no one else," Pruitt told lawmakers at last week's hearings.

Rep. Don Beyer, D-Va., who has pushed for investigations of ethical problems under Pruitt, said in a statement Tuesday that "Pruitt should be the next to go."

"Albert Kelly was never qualified to run Superfund, his banking ban was a huge red flag and his resignation is a positive development," Beyer said.