WASHINGTON - A dozen members of the National Guard have been removed from inauguration duty as the federal government screens troops involved for security concerns, senior U.S. defense officials said Tuesday, one day before President-elect Joe Biden is set to take over as commander in chief. 

The troops include at least two with possible sympathies for anti-government groups, said two U.S. officials, speaking on the condition of anonymity because of the sensitivity of the issue. Ten were removed for reasons that defense officials declined to detail but said did not involve extremism.

"These are vetting efforts that identify any questionable behavior in the past, or any potential link to questionable behavior not related to extremism," said Jonathan Rath Hoffman, chief Pentagon spokesman. He said the Defense Department is proactively removing people "out of an abundance of caution."

"There is going to be a continued look at this," Hoffman said. "Whether that is an internal DOD look within their chain of command or an investigation by others is something that is being determined."

Army Gen. Daniel Hokanson, the chief of the National Guard Bureau, declined to provide specifics about the troops alleged to have expressed common cause with anti-government groups but said they had made "inappropriate comments." One of them was flagged because of concern within his unit, while the other was reported anonymously, defense officials said. The other 10 guardsmen were identified by the FBI, Hokanson said.

The 12 represent a tiny fraction of the 25,000 guardsmen deployed in Washington for the inauguration because of the Jan. 6 assault on the U.S. Capitol by a mob that sought to stop the certification of Biden as the next president. The group, supporting President Donald Trump, launched an attack that led to the death of a Capitol Police officer, a woman who was shot by police, and three people who suffered medical emergencies.

An additional 2,000 active-duty service members are involved in the inauguration in ceremonial roles, said Army Maj. Gen. Omar Jones, the commander of the Military District of Washington. Those troops are credentialed by the Secret Service and have been reduced in number by about 3,500 over a typical inauguration because of the pandemic, he said.

Democratic lawmakers have sought vetting of National Guard members deployed for the inauguration since the riot, citing the arrest of numerous veterans in the mob, including a current member of the Virginia National Guard and an Army reservist. The names of guardsmen supporting the inauguration were sent to the FBI for screening as an additional precaution.

The scrutiny over extremist group activity within the ranks has helped generate leads from alert citizens, city officials said.

A passer-by at the D.C. Armory parking lot noticed a truck bearing a sticker for the Three Percenters, a right-wing anti-government group, and alerted Charles Allen, a District of Columbia councilman.

Allen referred the matter to city security officials and a senior D.C. Guard official, and it appeared that law enforcement was involved, he said. The Three Percenters "has no home in the District of Columbia," Allen said.

It is unclear whether the driver, whose truck bears Virginia plates, was one of the troops removed from duty. Cotton Puryear, a spokesman for the Virginia National Guard, declined to comment, citing cooperation with law enforcement.

For years, defense officials have said they do not tolerate extremism in the ranks - a point that senior defense officials repeated Tuesday.

After racial justice protests last summer, the Pentagon established the Department of Defense Board on Diversity and Inclusion, which found in its initial report in December that more research is needed to address the infiltration of extremist ideologies in the U.S. military.

During the inauguration, the guardsmen will play a key role in forming a fenced outer security perimeter that stretches for miles and includes the Capitol and the White House.

Most of the guardsmen - triple the number deployed during Trump's inauguration four years ago - are armed with rifles, with magazines of ammunition on hand but not in the weapon. Inside the perimeter, the Secret Service and other authorities will serve as additional security.

Guardsmen closer to the inner workings of the inauguration, such as those overseeing access points, may receive higher levels of screening, said Michael Taheri, a retired Air Force major general and former director of staff for the National Guard Bureau.

Background checks for service members have broadened in recent years to include social media activity and more frequent monitoring, Taheri said, mirroring how private companies comb online behavior for prospective hires.

"My guess is there is a lot of open stuff out there," he said.

The removal of the guardsmen comes after some leaders have taken exception to the additional vetting.

Gov. Greg Abbott, R-Texas, tweeted Monday that the screening of National Guard members for extremist ties is "the most offensive thing I've ever heard."

"I authorized more than 1,000 to go to DC," he tweeted. "I'll never do it again if they are disrespected like this."

Other officials have questioned whether having the National Guard involved is safe.

Rep. Steve Cohen, D-Tenn., said in a Monday interview on CNN that guardsmen who did not vote for Biden are in "the large class of people who might want to do something" threatening at the inauguration. Facing a backlash, Cohen said Tuesday in a statement that he appreciated the assurance that the National Guard's presence "provides that we will have a successful inauguration."

Jim Golby, an Army veteran who studies civil-military affairs at the University of Texas at Austin, said he is confident that the National Guard will perform professionally and admirably on Inauguration Day. The military, he said, "understands what is at stake and remains committed to carrying out its duties in a nonpartisan manner."

Golby said service members are accustomed to carrying out orders they may not personally like.

"There are always risks, and there is always the potential for individuals to make terrible choices," he said. "But I'm confident members of the National Guard are taking their duties seriously and doing all they can to mitigate potential risks."