The inspector general of the Defense Department has launched a probe into the military’s efforts to purge extremism from its ranks.

The objective is to determine whether the DOD and Military Services have implemented policies to "prohibit active advocacy and active participation related to supremacist, extremist, or criminal gang doctrine, ideology, or causes by active duty military personnel," the IG’s office said in a statement Thursday.

U.S. National Guard troops stand guard at the U.S. Capitol on Jan. 12,  in Washington, DC. The Pentagon is deploying as many as 15,000 National Guard troops to protect President-elect Joe Biden's inauguration on January 20, amid fears of new violence. (Photo by Tasos Katopodis/Getty Images)

U.S. National Guard troops stand guard at the U.S. Capitol on Jan. 12,  in Washington, DC. The Pentagon is deploying as many as 15,000 National Guard troops to protect President-elect Joe Biden's inauguration on January 20, amid fears of new violence. (Photo by Tasos Katopodis/Getty Images)

The statement said combating extremism is required under a DOD Instruction that regulates dissident and protest activities among servicemembers.

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The statement also said the IG could "revise or expand" the scope of the probe.

"We will include in our review the Military Departments and subordinate agencies that recruit, train, and sustain active duty military forces," Assistant IG Carolyn Hantz wrote in a memo. "We may identify additional offices and personnel during the evaluation."

The probe’s announcement follows the Jan. 6 harrowing siege by President Trump supporters of the Capitol to protest Congress’ ceremonial move to validate President-elect Joe Biden’s Electoral College victory.

Several accused rioters have been identified as former members of the military, including Ashli Babbitt, an Air Force veteran who was shot and killed by a Capitol Police officer at a barricaded door.

Larry Rendell Brock, 53, was arrested after his ex-wife turned him into the FBI after recognizing his image from photos taken of the Jan. 6 riot inside the U.S. Capitol building.

Larry Rendell Brock, 53, was arrested after his ex-wife turned him into the FBI after recognizing his image from photos taken of the Jan. 6 riot inside the U.S. Capitol building. (Justice Department)

The FBI also arrested a retired Air Force lieutenant colonel accused of breaching the Senate chamber in tactical gear and carrying zip tie handcuffs.

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Lawmakers, including Democratic Illinois Sen. Tammy Duckworth, a wounded veteran, have called on police and military authorities to investigate whether any active-duty members took part in the chaos.

"We must address deeply troubling reports that certain servicemembers and military retirees violated their oaths by participating in last week's violent insurrection," she tweeted Monday.

Fox News’ Lucas Tomlinson contributed to this report.