(CNN) – Domestic violent extremism is the “greatest threat” to the United States, Homeland Security Secretary Alejandro Mayorkas told lawmakers Wednesday during his first congressional hearing since taking office.

The threat comes from so-called lone wolves and individuals with loose associations following ideologies of hate and extremism who are “willing and able to take those ideologies and execute on them in unlawful, illegal, violent ways,” Mayorkas said.

His testimony comes a day after eight people were killed and one person was wounded in Atlanta-area shootings and in the wake of the January 6 insurrection at the US Capitol that officials believe was a coordinated attack.

Also on Wednesday, the Office of the Director of National Intelligence released an unclassified summary of a joint assessment of the national security threat posed by domestic violent extremism, as ordered by the White House in January.

Mayorkas said at the hearing that the domestic threat of a “lone wolf” is greater than the foreign threat at this time, when pressed by Democratic Rep. Elissa Slotkin, a member of the House Homeland Security Committee, although he pointed out it is always evolving.

“Right now, at this point in time, domestic violent extremism, the lone wolf, the loose affiliation of individuals following ideologies of hate and other ideologies of extremism that are willing and able to take those ideologies and execute on them in unlawful, illegal, violent ways is our greatest threat in the homeland right now,” Mayorkas said.

He told the committee that the events of January 6 were “heartbreaking.”

“I was brought to this country by my parents because of everything that the Capitol represents to the American people and because of everything that all of you on this committee do, which is to serve and represent the American people,” he said of Congress and the attack.

The secretary is conducting a review of the events that led up to the incident, he said, while being mindful of ongoing criminal investigations and prosecutions.

“It is very much a focus of the Department of Homeland Security, of mine personally,” he said, adding that domestic violent extremism is one of the “gravest and most persistent threats that we as a country face.”