The U.S. is tracking a high-altitude balloon flying over the Western part of the country, U.S. officials told CBS News. Military aircraft have spotted the balloon and determined it is not a threat, but its origin and purpose are still unknown, the officials said.

Sources familiar with the matter who spoke on the condition of anonymity said the balloon was drifting east in the jetstream on Friday. Earlier in the day, one official said the balloon was over Colorado. Its presence prompted enough concern that the military sent aircraft to investigate.

The developments come one year after tensions between the U.S. and China ratcheted to new heights after a Chinese balloon carrying sophisticated spying equipment flew over the continental U.S. for several days.