On December 11, 2012, the U.S. Air force launched its X-37b unmanned shuttle on its third mission. It is interesting how the shuttle went up one day before the North Korean's launched their rocket to place a satellite in orbit. However, it appears to be a coincidence since the X-37b was initially scheduled to launch on October 25, 2012, but was delayed due to rocket problems.
Even so, could the U.S. be monitoring this North Korean mission as well as others? We may never know since the X-37b missions are classified. However, the U.S. has other assets in the region and in orbit that can do this work just fine. As noted by Wired magazine:
The US has at
least two infrared sensors in HEO orbits as part of the
Space-Based Infrared System. Open source information
indicates that they are hosted on two classified
satellites, USA 184 and USA 200. The same satellites are
also believed to
carry a signals intelligence payload that can collect
electromagnetic emissions. Observations from amateur satellite
observers indicate that their orbits "hang" over Asia, indicating
that they likely could have been used to monitor the launch site
and observe the launch.