The U.S. Capitol was temporarily shut down Monday morning after a fire broke out several blocks away from the historic building.

The U.S. Secret Service tweeted that the incident is not believed to be a threat.

“Out of an abundance of caution, the U.S. Capitol complex was temporarily shut down,” the Secret Service said.

Early reports suggest the fire might be at a homeless encampment. It has since been extinguished.

Dark smoke began to drift over the building shortly after 10 a.m. Monday as a rehearsal for President-Elect Joe Biden’s inauguration was underway.

An emergency alert played across Capitol grounds as the smoke grew.

The alert said: “External security threat, no entry or exit is permitted. Stay away from exterior windows, doors. If outside, seek cover,” according to video and tweets by Global News reporters in Washington.

Rehearsal participants were evacuated into the building and held in the Capitol rotunda while the situation was investigated, witnesses told Reuters.

The U.S. Capitol Police said in a statement that all staff was advised to shelter in place while the incident was being investigated.

No injuries were reported.

Meanwhile, Tensions are high in Washington after thousands of Donald Trump’s supporters stormed the Capitol on Jan. 6, forcing lawmakers who were certifying Biden’s election victory into hiding in a harrowing assault on the heart of American democracy that left five dead.

About 25,000 National Guard troops have been deployed to the Capitol after intelligence sources suggest that Trump supporters might come back, and could be armed.

Biden’s inauguration rehearsal was moved from Sunday to Monday due to security concerns, officials had said.