Defense officials are concerned about a possible insider attack or other threat from military personnel involved in the security of President-elect Joe Biden's inauguration. Thus, the FBI checks all 25,000 National Guard soldiers who arrived in Washington to participate in the event.

The massive event reflects the extreme security concerns that gripped Washington after the January 6 Capitol riots.

Army Secretary Ryan McCarthy told The Associated Press that officials are aware of the potential threat and warned commanders to be on the lookout for any issues within their ranks as the inauguration draws near. So far, however, they have said there is no evidence of any threats, and officials said the inspection did not reveal any issues they knew about.

Nearly 25,000 National Guard troops are arriving in Washington from across the country - at least two and a half times more than at previous inaugurations. And while the military regularly checks military personnel for extremist ties, the FBI screening is in addition to any monitoring.