WASHINGTON, March 3 (Xinhua) -- U.S. Capitol Police said on Wednesday that it has learned of a "possible plot to breach the Capitol" by a militia group driven by a conspiracy theory suggesting former President Donald Trump would return to power on March 4.

The Capitol Police said in a statement that it has obtained intelligence about the plot planned by an "identified militia group" and already made "significant security upgrades" to the Capitol starting earlier this week.

The security upgrades include "establishing a physical structure and increasing manpower to ensure the protection of Congress, the public and our police officers," said the statement, adding that the force is "working with our local, state, and federal partners to stop any threats to the Capitol."

"We are taking the intelligence seriously. Due to the sensitive nature of this information, we cannot provide additional details at this time," the statement said.

Some QAnon conspiracy theorists have said that Trump will be inaugurated on March 4 because that was the original Inauguration Day for presidents until 1933, when it was moved to Jan. 20.

However, a source told CNN that it is mostly online talk and not necessarily an indication anyone is coming to Washington to act on it.

During a Senate hearing on Wednesday, Melissa Smislova, acting intelligence chief of the Department of Homeland Security (DHS), confirmed to lawmakers that the DHS and Federal Bureau of Investigation (FBI) had internally issued a joint intelligence bulletin about "extremists discussing March 4, and March 6."

Security has been tight around the Capitol since the Jan. 6 riot which interrupted Congress' electoral vote count of U.S. President Joe Biden's victory. Five people died in the attack, including a Capitol police officer.

Christopher Wray, director of the FBI, said on Tuesday that the law enforcement agency classifies the Jan. 6 Capitol riot by Trump's supporters as domestic terrorism.