"Over the last several weeks, we have witnessed brazen acts of violence, committed in places that many would have considered unthinkable," Holder told the Washington Lawyers Committee for Civil Rights and Urban Affairs.
He cited separate attacks over a two-week period that killed a young soldier, an abortion provider and a guard at the U.S. Holocaust Memorial Museum.
Federal agents and prosecutors are already involved in the local investigations of each attack.
The violence, he said, "reminds us of the potential threat posed by violent extremists and the tragedy that ensues when reasoned discourse is replaced by armed confrontation."
In order to stop that violence, he said, Congress should past an updated version of hate crimes legislation, in order to more effectively prosecute those who commit violent attacks based on gender, disability, or sexual orientation.
The growing number of hate crimes against Hispanics also shows the need for tougher laws, Holder said.
"We will not tolerate murder, or the threat of violence, masquerading as political activism," Holder said. "So let me be clear, the Justice Department will use every tool at its disposal to protect the rights ensured under our Constitution."
Earlier, a leading civil rights coalition says there has been an increase in white supremacist activity since the election of the first African-American president.
The Leadership Conference on Civil Rights Education Fund reported Tuesday that the economic downturn and fear of immigrants also contributed to the increase.
The report comes a week after a white supremacist killed a security guard at the U.S. Holocaust Museum.
The coalition reported the U.S. now averages a hate crime nearly every hour of every day. A special concern is the rising number of hate crimes committed against Hispanics and gays.
Separately, a national advocacy group says the number of lesbian, gay, bisexual and transgender people killed in .
The National Coalition of Anti-Violence Programs released its report Tuesday. It says last year's 29 killings is the highest it has recorded since 1999. It documented the same number of slayings then.
The New York-based coalition says the overall number of victims who reported gay bias violence in 2008 increased by 2 percent.
The coalition says its figures are more accurate than those from law enforcement agencies. As an example, the group says the FBI doesn't record bias crimes against transgender people because gender identity isn't covered by federal hate-crime law.
Last week, CBS News correspondent Bob Orr reported that in the past eight years, the number of hate groups in America has exploded - up 50 percent - from 602 in 2000 to 926 last year.