China has rapidly expanded it military in recent years and Keating said the US was "paying close attention to the development of China's military capability".
Pointing to a double digit growth in China's military spending over the past decade, he said China's armed forces were developing "impressive capabilities".
Of particular concern to the US, Keating said, were developments in long-range cruise and ballistic missiles, anti-satellite technology and its use, and "area denial weapons" – a possible reference to chemical weapons.
"If we don't see what it is they are developing we may tend to assume a little more serious or potentially destabilisng military capabilities," he said.
In November China blocked a port call by the aircraft carrier USS Kitty Hawk and five support ships for what US officials said was a scheduled Thanksgiving holiday visit.
The same week two US minesweepers were also turned away after seeking shelter during a storm – an incident that sparked particular criticism from Keating at the time.
|China's increased military spending has |
set alarms ringing in the US [EPA]
Speaking to reporters on Tuesday, Keating said he had brought up the issue in talks with Chinese military officials.
"We were unhappy that the visit was cancelled, we have discussed it," he said, adding that incidents pointed to a "recurring theme – the development of trust and confidence and transparency".
He continued: "Increased transparency can yield to greater trust - that reduces the potential for misunderstanding, misunderstanding can lead to conflict or crisis, and that is very much not in our interest. We want peace and stability in the region."
China gave no official reason for the decision to refuse the port visits, other than to say procedures had not been followed.
There have been hints, however, that the decision was triggered by a visit to the US by the Dalai Lama, the exiled Tibetan spiritual leader, and anger over US arms sales to Taiwan.
China views the Dalai Lama as what it calls a "splittist", intent on separating Tibet from China, and regards Taiwan as a breakaway province that it will eventually reclaim, by force if necessary.
Keating's visit to China is his second since taking up his post early last year.
Based in Hawaii, the Pacific Command oversees busy trade routes that feed China's booming economy and the potentially unstable Taiwan Strait that divides self-ruled Taiwan from mainland China.