Two days ahead of US President Elect Joe Biden's inauguration ceremony, the US Capitol was temporarily put on lockdown on Monday due to an 'external security threat'.

Participants in a rehearsal for Biden's inauguration ceremony were evacuated from the West Front of the US Capitol on orders of security officials after a fire in a homeless encampment, officials said.

Those who had gathered for a walk-through, including a military band, were directed to head indoors and moved in the directed of a secure location inside the US Capitol complex.

People involved in the rehearsal said security officials yelled "this is not a drill."

Four law enforcement officials told an international news agency, there had been a blaze several blocks over and the rehearsal was evacuated in an abundance of caution.

The US Capitol complex and surrounding areas have been locked down after a riot there January 6.

(With inputs from agencies)