GRAND FORKS (AP) - Reports of violent crime have been on the rise in North Dakota's three largest cities the past two years, though authorities say that does not necessarily mean that Grand Forks, Fargo and Bismarck are more dangerous places than they used to be.

The violent crime category includes murders, robberies, rapes and aggravated assaults.

In Grand Forks, the total violent crimes reported the past two years averaged 105 per year, compared with an average of 65 in 2002-05.

Fargo had an average of 199 violent crimes reported each of the past two years, compared with 147 per year the previous four years.

Bismarck police received an average of 120 reports of violent crime in 2007 and 2006, compared with only 42 on average from 2002-05.

Grand Forks Police Chief John Packett said the numbers do not tell the entire story. "The total numbers are relatively low, although they are serious," he said.

Grand Forks has about 52,000 residents, Fargo about 92,000 and Bismarck about 58,000. Packett said Grand Forks' rate of serious crime per 100,000 people is half that of the national average. He also said that two years of data might not be enough to show trends.

"As the numbers come in, if we continue to see these signs, we need to take a hard look at not only the economic but the demographics and why the community may be changing and why we see those spikes" in reported crime numbers, he said.

Packett said it also is difficult to compare crime in different cities. Even though the three police departments use the FBI's Uniform Crime Reporting system, each police department might still log some reports differently, he said.

The FBI also warns on its Web site against quick comparisons of national statistics with local ones, or comparing cities, because of the many variables involved.