WASHINGTON - Top US military officer Mike Mullen on Wednesday said Secretary of Defense Robert Gates' trip to China, which concluded earlier in the day, enhances military to military relations between the two countries.

"I think his visit enhances the relationship," Joint Chiefs of Staff Chairman Mullen said. "From an overall strategic point of view, again I've long ... been a believer in the importance of the strength of the relationship of these two countries."

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Speaking at the Foreign Press Center in Washington, Mullen said the two countries' military relationship has long lagged behind their robust economic ties.

"Tied to that prosperity, there needs to be security, they go hand in hand," said Mullen, noting having a strong security relationship is equally important as having a strong economic relationship.

Mullen said the strengthening of military to military relationship between the two countries is critical, as "there's a great deal, quite frankly, that we don't understand about each other."

"So having a strong security relationship is equally important to having a strong economic relationship. I think that's the relationship we are, certainly, working toward," said Mullen.

Gates paid a four-day visit to China from January 9 to 12.