 -- China has placed some of its bomber fleet on heightened alert status, according to U.S. officials, but it is unclear what may have prompted the move. One official said the heightened alert could indicate contingency plans to react to a situation with North Korea, while another official said it is possible that China could be preparing for a military exercise.

U.S. officials told ABC News on Wednesday that China had elevated the alert status of its land attack, cruise missile-capable bombers.

It also initiated maintenance for an unusual number of fighter/bomber aircraft, officials said.

One U.S. official said additional space was also being set aside for aircraft at seven airfields. Another U.S. official said the alert status was not restricted to one particular region of China but spread out across the country.

There were varying opinions as to what may have prompted the heightened alert status. The move comes at a time when tensions on the Korean peninsula are higher. North Korea has continued to engage in provocative behavior that is in defiance of international bans. North Korea has recently launched ballistic missile tests and threatened to conduct its sixth underground nuclear test.

One official said placing these aircraft on a higher alert status could reduce the Chinese Air Force's response time if they had to react to an incident in North Korea or elsewhere in the region.

Another official said the reason may be more benign: a higher alert status is also sometimes used ahead of a future drill or exercise. This official noted that the seven airfields affected by the higher status are spread out across China and not in the northeastern part of China, which is closest to North Korea.

The official indicated that generally, Chinese readiness statuses will ebb and flow during training cycles.