WASHINGTON (AFP) - There are no borders in the world of Pokemon Go.

But two young fans of the hit smartphone game were so preoccupied with catching cartoon monsters that they wandered across the US-Canada border in real life.

US Border Patrol agents spotted the pair illegally walking from Canada into the US on Thursday evening, the agency's office in Sweetgrass, Montana said in a statement.

"Both juveniles were so captivated by their Pokemon Go games that they lost track of where they were. They crossed the international border inadvertently, but agents were able to reunite them with their mother," public affairs officer Michael Rappold was quoted as saying.

It was a happy ending for the two youngsters.

Other Pokemon Go players have not been so lucky, finding themselves the victims of robbery or violent crimes. Fans have also been blamed for causing traffic accidents.

In Indonesia, a French player was stopped and questioned for several hours after the app led him into a military base.

The free app uses satellite locations, graphics and camera capabilities to overlay cartoon monsters on real-world settings, challenging players to capture and train the creatures for battles.