DHS Secretary Alejandro Mayorkas referred to the January 6 deadly attack on the US Capitol by supporters of former president Donald Trump, saying it highlighted the threat of US-based extremists.
He made the remarks as concerns over white supremacist beliefs at immigration enforcement agencies within DHS have risen, with many attributing the domestic extremism to Trump's racist rhetoric.
A group of senior DHS officials "will immediately begin a comprehensive review of how to best prevent, detect, and respond to threats related to domestic violent extremism within DHS," the department said in a statement on Monday.
The threat of violent extremism within the ranks of US federal agencies came to light after the Pentagon acknowledged earlier this year that far-right and white supremacist extremists were actively recruiting in the US military, announcing an investigation into the extent of extremist ideologies among active-duty personnel.
Fears over white nationalism and other extremism in the ranks of US federal agencies spiked after many people who took part in the January violent Capitol attack were found to be active military personnel and veterans.
The unprecedented attack was incited by Trump and left five people dead.
Mayorkas said domestic violent extremism "poses the most lethal and persistent terrorism-related threat to our country today," adding that "hateful acts and violent extremism will not be tolerated" within DHS.
President Joe Biden called for funding to investigate any complaints of white supremacist beliefs at immigration enforcement agencies within DHS in his first budget proposal, which was unveiled this month.
Biden also ordered the director of national intelligence to work with the FBI and Homeland Security Department on a comprehensive assessment of how the government combats extremism.
The administration followed up with an intelligence report delivered to Congress last month that identified white supremacists and militia groups as top national security threats.