The Biden administration is creating a new unit in the justice department to counter domestic terrorism following the deadly US Capitol attack by supporters of Donald Trump, a senior official said on Tuesday.

“We face an elevated threat from domestic violent extremists,” Matthew Olsen, assistant attorney general of the national security division, told a hearing held by the Senate judiciary committee.

Olsen was testifying days after the US observed the first anniversary of the violent attack on Congress, in which Trump supporters sought to stop certification of Joe Biden’s election victory.

Olsen said the number of FBI investigations into suspected domestic violent extremists had more than doubled since the spring of 2020.

In November, a top FBI official told Congress the bureau was conducting around 2,700 investigations related to domestic violent extremism.

Olsen defined such extremists as “individuals in the United States who seek to commit violent criminal acts in furtherance of domestic social or political goals”.

“Domestic violent extremists are often motivated by a mix of ideologies and personal grievances,” he said. “We have seen a growing threat from those who are motivated by racial animus, as well as those who ascribe to extremist anti-government and anti-authority ideologies.”

The attorney general, Merrick Garland, told lawmakers last May domestic violent extremist groups, particularly white supremacists, posed a growing threat to the US.

The DoJ national security division has a counter-terrorism section. Olsen told the committee he decided to create a specialised domestic terrorism unit “to augment our existing approach”.

Olsen said the new unit will be housed within the national security division and will work to “ensure that these cases are properly handled and effectively coordinated” across the department and around the country.

Five people died around the Capitol attack and more than 100 police officers were hurt. The DoJ has brought criminal charges against more than 725 participants.

Some of the defendants are members or associated with far-right groups or militia including the Proud Boys, the Oath Keepers and the Three Percenters.