The murder rate jumped by more than 10 percent among dozens of large U.S. cities since 2004, a study shows in the latest sign of the end of a national lull in violent crime.

Robberies also spiked, as did felony assaults and attacks with guns, according to the report to be released Friday by the Police Executive Research Forum, a Washington-based law enforcement think tank.

FBI data similarly has shown a rise in violent crime — if not as dramatic — since 2004. The Justice Department says crime was historically low that year.

"Two years worth of double-digit increases in violent crime demonstrates an unmistakable change in the extent and the nature of crime in America," said Chuck Wexler, executive director of the nonprofit think tank that is funded in part by the Justice Department, as well as corporations and private foundations.

"There are those that say this is a statistical blip, an aberration," Wexler said. "After two years, this is no aberration."

The report surveyed crime rates in 56 large U.S. metropolitan areas including Los Angeles, Chicago, Dallas and Washington. It did not include violent crime rates in New York, the nation's largest city, which did not participate in the voluntary survey. An advance copy of the report, titled "Violent Crime in America: 24 Months of Alarming Trends," was obtained by The Associated Press.

The report compared crime statistics from 2004, 2005 and 2006 and tracked how much they had changed over the 24 months beginning Jan. 1, 2005.

Justice spokesman Dean Boyd called the department "concerned about the increase in violent crime in some cities and towns" as was reported in FBI data released last fall. Attorney General Alberto Gonzales has asked Congress to spend $200 million next year to help cities and regions combat gangs, illicit drugs and gun offenses.

"The Department of Justice is committed to ensuring the safety of every American city and town," Boyd said.

The forum's study found:

— _Forty of the 56 surveyed police departments, or 71 percent, saw homicide rates increase since 2004. That translated into an overall 10.2 percent jump in murders. Between 2005 and 2006, the increase in murders was much lower: 2.8 percent.

— Robberies rose among the cities by 6 percent since 2005 and 12 percent since 2004. Between 75 and 80 percent of the departments surveyed saw a spike in robberies.

— Felony assaults dipped slightly, by 2 percent, between 2005 and 2006, but rose slightly, by 3 percent, since 2004.

— Gun assaults saw a 1 percent boost from 2005 but spiked by nearly 10 percent during the 24-month period.

The Justice Department has been keeping a close eye on crime rates after seeing a 2.2 percent rise nationwide in rapes, murder, robbery, aggravated assault and other violence in 2005 — the first increase since 2001.

Last fall, mayors and police chiefs reported seeing recent spikes in violent crime, calling for greater support from federal law enforcement agencies that have been distracted by counterterror missions since the Sept. 11, 2001, attacks.