Washington (CNN) -- The number of violent crimes in the United States decreased in the first six months of the year, continuing a downward trend, according to preliminary data released Monday by the FBI.
Overall, violent crimes were down 6.4%, while property crimes fell 3.7% when compared with figures from the first six months of 2010.
The report is based on information from more than 12,500 law enforcement agencies that submitted data to the FBI.
"Although we can all be encouraged that violent crime rates continue to decline nationwide, it is clear that we must remain vigilant and more work remains to be done," said Attorney General Eric Holder in a statement released with the semiannual statistics. "In recent months, we have seen an alarming spike in law enforcement fatalities and the number of line-of-duty law enforcement deaths. This is appalling and unacceptable."
Holder credited state and local authorities and federal agents with increased community participation. He specifically cited efforts to target violent criminals involved in gang activity, organized crime networks and drug trafficking organizations.
The FBI says all four offenses in the violent crime category -- murder, forcible rape, robbery and aggravated assault -- decreased in the first half of 2011. The number of murders declined 5.7%; rapes, 5.1%; robbery, 7.7%; and aggravated assault, 5.9%.
Cities with populations between 50,000 and 99,999 recorded the largest decrease in violent crime at 7.2%, according to the FBI.
When broken down into regions, violent crime dropped across the country with the largest decrease in the Midwest at 9.7%, followed by the West at 6.6%, the South at 5.8% and the Northeast at 3.6%.
Property crime showed slightly less decline in the categories of burglary, larceny and motor vehicle theft. The FBI said burglary offenses dropped 2.2%, larceny dropped 4% and motor vehicle theft decreased 5%.
Arson offenses, which are collected separately, dropped 8.6% in the first six months of 2011 in every region of the country.