PORTSMOUTH, N.H. – City police have arrested two sex offenders accused of targeting teenagers in the past two weeks.

One was accused of spending a night in a motel with a 15-year-old boy. The other was accused of holding a knife to the throat of a 16-year-old girl while fondling her.

Since January 2006, police have arrested 29 people accused of molesting a child, possessing child pornography or using the Internet to lure children for sex. That’s an average of two arrests each month in a city of just 21,000 people.

Police say the numbers are higher than elsewhere in the state in part because of the city’s location on Interstate 95 between Maine and Massachusetts.

They say some sexual predators who plan to re-offend leave their home states and stay in shelters, cheap motels and rooming houses in Portsmouth without registering with police.