WASHINGTON (AP) — The head of the U.S. Capitol Police defended his department's response to the storming of the Capitol, saying Thursday that officers “acted valiantly when faced with thousands of individuals involved in violent riotous actions.” Washington's mayor called the police response “a failure.”

Chief Steven Sund, in his first public comment on the mayhem from Wednesday, said in a statement that rioters “actively attacked” Capitol police and other law enforcement officers with metal pipes, discharged chemical irritants and “took up other weapons against our officers.”

The siege, as the House and Senate were affirming President-elect Joe Biden's election victory, was “unlike any I have ever experienced in my 30 years in law enforcement here in Washington, D.C.,'' said Sund, a former city police officer. ”Make no mistake: these mass riots were not First Amendment activities; they were criminal riotous behavior. The actions of the USCP officers were heroic given the situation they faced.''

Lawmakers from both parties have pledged to investigate law enforcement's actions and questioned whether a lack of preparedness allowed a mob to occupy and vandalize the building.

Mayor Muriel Bowser joined in the criticism of the police response. "Obviously it was a failure or you would not have had people enter the Capitol by breaking windows and terrorizing the members of Congress who were doing a very sacred requirement of their jobs.''

A large crowd of Trump supporters had rallied near the White House on Wednesday morning, and the president told them that he would go with them to the Capitol. He didn’t. Instead he sent them off with incendiary rhetoric. “If you don’t fight like hell, you’re not going to have a country anymore,” he said. “Let the weak ones get out,” he went on. “This is a time for strength.”

Capitol Police, who are charged with protecting Congress, turned to other law enforcement for help with the mob that overwhelmed the complex and sent lawmakers into hiding. Both law enforcement and Trump supporters deployed chemical irritants during the hourslong occupation of the complex before it was cleared Wednesday evening.

Four people died, including a woman who was shot and killed by police inside the Capitol. Three other people died after “medical emergencies” related to the breach, said Robert Contee, chief of the city’s Metropolitan Police Department.

D.C. police said Thursday that 68 people were arrested, while Capitol police said 14 were arrested, most for unlawful entry. More than 50 Capitol and D.C. police were injured, including several who were hospitalized, Sund said.

Rep. Zoe Lofgren, D-Calif., chairwoman of the House Administration Committee, said the breach “raises grave security concerns.″ She said her committee will work with House and Senate leaders to review the police response — and its preparedness.

Rep. Val Demings, D-Fla., a former police chief, said it was “painfully obvious" that Capitol police “were not prepared” for what took place Wednesday. "I certainly thought that we would have had a stronger show of force, that there would have been steps taken in the very beginning to make sure that there was a designated area for the protesters in a safe distance from the Capitol.''

In an interview with MSNBC, Demings said it appeared police were woefully understaffed, adding that "it did not seem that they had a clear operational plan to really deal with” thousands of protesters who descended on the Capitol following Trump's complaints of a "rigged election.''

The rioters were egged on by Trump, who has spent weeks falsely attacking the integrity of the election and had urged his supporters to come to Washington to protest Congress’ formal approval of Biden’s victory. The protests interrupted those proceedings for nearly seven hours; lawmakers finished up early Thursday.

The mob broke windows, entered both the Senate and House chambers and went into the offices of lawmakers, including House Speaker Nancy Pelosi, D-Calif.

Demings said there were "a lot of unanswered questions and I’m damn determined to get answers to those questions about what went wrong.''

Rep. Tim Ryan, D-Ohio, suggested there could be leadership changes at the Capitol police.

“I think it’s pretty clear that there’s going to be a number of people who are going to be without employment very, very soon because this is an embarrassment both on behalf of the mob, and the president, and the insurrection, and the attempted coup, but also the lack of professional planning and dealing with what we knew was going to occur,” Ryan said.

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Associated Press writer Michael Balsamo contributed to this report.