US Capitol Police Chief Steven Sund has announced that would resign this month after he faced criticism for failing to prevent supporters of President Donald Trump from storming the building.

Sund’s resignation came hours after House Speaker Nancy Pelosi and Senate Democratic Leader Senator Chuck Schumer on Thursday demanded his resignation and said that he would be fired if he did not resign.

“It has been a pleasure and a true honour to serve the United States Capitol Police Board and the Congressional community alongside the men and women of the United States Capitol Police," Sund said in a letter to Capitol Police Board. Other members of the Board are also resigning from their positions.

“As discussed, I will transition into a sick leave status effective January 17, 2021, until I exhaust my available sick leave balance of approximately 440 hours,” he said.

In an unprecedented assault on democracy in the US, thousands of supporters of outgoing President Trump stormed the Capitol building on Wednesday and clashed with police, interrupting a constitutional process by Congress to affirm the victory of President-elect Joe Biden and Vice President-elect Kamala Harris in the election.

The United States Capitol Police Labor Committee also called for Sund's resignation.