COLORADO SPRINGS, Colorado (AP) -- The North American Aerospace Defense Command monitored the launches of a series of missiles from North Korea Tuesday but soon determined they weren't a threat to the United States, a spokesman said.

"We were immediately aware of six launches from North Korea," said Michael Kucharek, a spokesman for NORAD and the U.S. Northern Command.

NORAD, a joint U.S. and Canadian command, monitors the skies for threats like missiles, aircraft and space objects from inside the Cheyenne Mountain Air Force Station. It relies on radar and satellites and other systems, Kucharek said.

"We continue to monitor the situation (in North Korea) and are looking for and will defeat any threat to the United States and its territory," he said.

U.S. officials said that North Korea launched a long-range missile that may be capable of reaching the United States, but that the missile failed after 35 or 40 seconds.

NORAD was also busy monitoring the space shuttle launch on Tuesday, Kucharek said.

Cheyenne Mountain, which contains elements of both NORAD and Northern Command, was placed on heightened security within the past couple of weeks, Kucharek said, but he wouldn't say whether the change was made because of rumors of a possible missile launch in North Korea.

The current "Bravo-Plus" status is slightly higher than a medium threat level, he said. Kucharek said it only pertained to the level of security at Cheyenne Mountain and it didn't change operations at NORAD or Northern Command. Founded after the September 11 terrorist attacks, Northern Command is responsible for defending U.S. territory.

"We continue to perform the mission that's been assigned to us. We are always on alert," he said.