Washington —- As the Arctic ice cap shrinks, the Pentagon is eyeing the expanding navigable waters as possible entry points for security threats that must be monitored more closely, the chief of the U.S. Northern Command says.

Air Force Gen. Gene Renuart also said defense officials are working with the Federal Aviation Administration and Canadian authorities to determine how unmanned aircraft can be used to monitor the northern border without interfering with busy commercial air traffic routes.

For much of the last 18 months, the military has been more visibly focused on the country's southern border —- dispatching National Guard troops to help patrol there while additional border guards were trained.

But Renuart said there will be increased military activity along the expansive northern boundary and beyond, including efforts to use more high-tech sensors and cameras like those developed for the Iraq and Afghanistan wars.

"The Arctic is a new area that is important to us because of the changes in ice flows," said Renuart. The shift, he said, means that Northern Command will beef up its maritime surveillance.

Renuart's comments came as Defense Secretary Robert Gates was traveling Monday to Colorado Springs, Colo., for the 50th anniversary of NORAD, the North American Aerospace Defense Command.

Scientists have said the ice in the north shrank to a record low last summer, a change many attribute to global warming. And as the ice opened up, traffic in the Arctic region grew, particularly along the northwest passage.

"Last year, during the summer months, where the ice had retreated we began to see some tourist ships, cruises, in the region," Renuart said.

For ships headed from the Pacific to Europe, traveling through the northwest passage saves time and valuable energy costs.

That traffic increase has coincided with greater international interest in potential energy resources in the Arctic, prompting more exploration.

"All of this has implications that there could be security concerns," Renuart said.

The U.S. and Canada already have said there are plans to use unmanned aerial vehicles along the more than 5,000-mile long northern border. The military has chosen a base in Grand Forks, N.D., to base the Predator drones for that mission, largely due to its central location.

Renuart said the effort has been slowed as officials try to resolve air traffic congestion issues and train UAV operators to fly the drones in the north's more heavily wooded terrain.