The FBI says violent crime increased more than 15 percent last year in North Dakota, a spike that worries Attorney General Wayne Stenehjem.

"One area of great concern is aggravated assault, which has trended up since 1999," Stenehjem said.

The spike could be attributed to an increase in illicit drug use in the state, he said.

"We think it is probably drug use, particularly methamphetimine, which tends to make people more desperate and more violent," Stenehjem said.

The FBI statistics show a total of 813 violent crimes reported in the state last year, compared to 706 in 2005.

Aggravated assault crimes rose from 217 in 1999 to 525 last year, Stenehjem said.

The attorney general said North Dakota remains among the safest states in the nation. The FBI's report ranks North Dakota 49, behind Maine, with the fewest number of violent crimes, he said.

The state reported fewer crimes in the category of murder and non-negligent manslaughter - with eight last year compared to 12 the year before.

Stenehjem said the state has averaged about 11 homicides annually for more than a decade.

The number of forcible rapes increased to 193 last year from 180 in 2005. "That's concerning," Stenehjem said. "It may be that there are more people willing to report the crime - we hope that's at least part of the case."

Nationally, the FBI said violent crime rose nearly 2 percent last year.

The state's annual Bureau of Criminal Investigation report will be released in a few weeks. It includes all reporting law enforcement agencies over a more lengthy reporting period, and factors in crime on North Dakota's American Indian reservations, Stenehjem said.

The roots of most crimes in North Dakota - and elsewhere - are drugs and alcohol, Stenehjem said.

"Certainly, if there were no drugs or alcohol, we could close up most of the penitentiary and most of my agents would be looking for work, and would be happy to be doing so," Stenehjem said.