The US Department of Defence is “doing everything it can” to root out extremism in the ranks after some troops and veterans joined the Capitol siege on January 6, the Pentagon said on Thursday.
Members of the military are continuously evaluated for involvement in white supremacy, criminal gangs and hate groups, said Garry Reid, the director for defence intelligence.
That included those in the National Guard now patrolling Washington to provide security for president-elect Joe Biden’s inauguration on Wednesday.
Scrutiny includes background investigations when enlisting and insider threat programmes.
The agency is assisting federal law enforcement with investigations into the Capitol breach.
"Simply put, we will not tolerate extremism of any sort [in the Department of Defence]," Mr Reid said.
The Pentagon inspector general announced on Thursday that the agency will open an investigation into white supremacy and gang activity.
The inquiry will review how well the military prohibits advocacy and participation related to supremacist, extremist or criminal gang ideology, said Carolyn Hantz, assistant inspector general for evaluations.
The review "was planned oversight work based on our situational awareness about what is going on [in the Department of Defence]," said Dwrena Allen, spokeswoman for the inspector general's office.
A group of Democratic senators and independent Bernie Sanders on Thursday wrote of their concerns on the matter to acting Pentagon inspector general Sean O’Donnell.
“The issue of white supremacy and extremist ideology within the ranks of our military is not new, but the attack on the Capitol makes clear this alarming trend must be immediately addressed,” they wrote.
Air Force veteran Ashli Babbitt was fatally shot by Capitol security as she and other rioters tried to break into the House chamber.
The Army is investigating an officer who led a group to the pro-Trump rally before the siege and a retired Air Force colonel who was arrested after being photographed inside the Capitol with a military-style helmet and zip ties.
It is also investigating a Navy veteran in a buffalo headdress who was arrested after breaking into the Senate chamber.
The military recorded a rise in extremist activity over the past year among active-duty troops and veterans, as the wider American society became politically polarised, a senior defence official said.
Increases in military extremism are partly due to more internal reporting, the official said.
But the Pentagon could not provide statistics on the number of cases, nor how they were resolved.
Acting Defence Secretary Christopher Miller ordered a review last month of the Pentagon’s policies on extremism and hate groups. The report, with recommendations, is due in June.
Pentagon leaders moved to rename bases that honour Confederate figures last year as protests over racial inequality rocked the country.
The move was strongly opposed by President Donald Trump but Congress ordered it to proceed as part of the annual defence policy law that was approved despite his veto.