Violent crimes in the United States has risen by 1.2 per cent in 2012 compared from a year ago, according to the Preliminary Annual Uniform Crime Report released by the FBI on Monday.

Based on information gathered from 13,770 law enforcement agencies, the uptick was likewise the first in a span of six years.

The increase in major crimes occurred in the cities with populations ranging 500,000 to one million people. In these areas, violent crime jumped by 3.7 per cent, as well as murder rates by 12.5 per cent.

By region, the US' West region registered the largest increase in violent crimes among its four regions. The West recorded a 3.3 per cent jump, the Midwest up by 1.3 per cent and the South by 0.6 per cent. It was only the Northeast that registered a 0.6 per cent decrease in violent crime offenses.

The FBI report likewise noted an increase of 3.2 per cent in forcible rape offenses in cities with populations of 1 million and over, which in those with populations of only 25,000 to 49,999 inhabitants, forcible rapes slid by 3.5 per cent.

The last time the occurrence and rate of violent crimes grew in the entire US was in 2006. The rate of violent crimes that year jumped 1.9 per cent. But before and after that particular year, the rate of violent crimes was only minimal.

"We probably now have answered the question of how low it can go, and we may be bouncing off the bottom now," Dennis Jay Kenney, a professor at John Jay College of Criminal Justice in New York, was quoted by the New York Times.

Still, much has to be studied. "We probably need another year to tell if we've got a pattern here," he said.

Experts theorised one reason for the rise could be the number of patrolling police officers. Some metropolitan areas have been forced to slash spending following years of recession.