The report by the Police Executive Research Forum (PERF), a Washington-based law enforcement think tank, said the murder rate in 56 large metropolitan areas, including Los Angeles, Chicago, Boston and Detroit, has jumped overall by 10 percent between 2004 and 2006.

"The 24-month trend toward increasing violence is disturbing news, because the United States enjoyed astonishing declines in crime during the mid- to late-1990s, followed by a leveling-off in the early 2000s," Chuck Wexler, executive director of PERF, said in a statement.

He warned that a recent summit on violent crime held by law enforcement officials from across the country concluded that there was a "gathering storm" of increasing violence in America.

Among the major cities that have recorded an increase in murders between 2004 and 2006 are Chicago, Illinois (up 3.8 percent), Houston, Texas (up 11.9 percent), and Miami, Florida (up 42.6 percent).

The cities of Newark, New Jersey, and Orlando, Florida, meanwhile recorded their highest number of murders ever in 2006 -- 105 in Newark and 49 in Orlando.

The city of Boston, in Massachusetts, saw an 11-year high in homicides in 2006 with 75 people murdered.

Several cities experienced a triple-digit jump in homicides, including Charleston, South Carolina (130 percent higher), Fairfax County in Virginia (up 111 percent) and Orlando (up 188 percent).

The PERF statistics confirm similar figures released by the Federal Bureau of Investigation in December.

That data showed a rise in violent crime with 32,840 murders recorded in the US in 2004-2005, and 818,592 robberies reported.