WASHINGTON — U.S. defense officials say they are worried about an insider attack or other threat from service members involved in securing President-elect Joe Biden’s inauguration.

That concern is prompting the FBI to vet all 25,000 National Guard troops coming into Washington for the event.

The massive undertaking reflects the extraordinary security concerns that have gripped Washington following the deadly Jan. 6 insurrection at the U.S. Capitol by pro-Trump rioters.

The vetting also underscores fears that some of the very people assigned to protect the city over the next several days could present a threat to the incoming president and other VIPs in attendance.