The nation's capital and cities across the country ramped up security ahead of US President-elect Joe Biden's inauguration, amid warnings of possible political violence even after the Jan 20 swearing-in.

Delta, Alaska, American, and United Airlines announced on Thursday they will not allow travellers flying to Washington area airports to check firearms on its flights before the inauguration.

Delta chief executive Ed Bastian told CNBC his airline had placed passengers on a no-fly list for their involvement in disruptive incidents...