America's highest ranking military officer is in South Korea for the inauguration of a new commander of U.S. forces in the country.

Joint Chiefs Chairman Mike Mullen traveled to Seoul after a four-day to visit to China, in which he was given rare access to that country's nuclear missile and submarine bases.

In South Korea Thursday, Mullen looked on as General James Thurman took command of more than 28,000 U.S. forces in the country. Thurman, who succeeds General Walter Sharp, said the U.S.-South Korean alliance “stands ready to counter any provocation intended to destabilize the Korean peninsula.”

Mullen concluded his China tour Wednesday with a visit to a submarine base in Shandong province, east of Beijing. Earlier, he was permitted to visit an air base housing China's advanced Su-27 jet fighters and visit the Second Artillery Force, which commands China's nuclear arsenal.

The state-operated China Daily newspaper said the visits were arranged “to highlight openness, transparency and self-confidence of China's military power.” It said the visits reciprocated a trip in May by Chinese armed forces commander Chen Bingde to the largest U.S. naval base.

China's official Xinhua news agency quoted Mullen saying his visit had helped to ease some of his concerns about a lack of transparency regarding China's military expansion. He said he regarded the exchanges as “a very positive step.”