Chinese Vice President Xi Jinping is urging China and the United States to deepen mutual trust and expand common ground to improve military cooperation.

Xi spoke Monday in Beijing with visiting U.S. Admiral Mike Mullen, Chairman of the U.S. Joint Chiefs of Staff. He hailed what is widely seen as improving Sino-U.S. ties, saying they represent one of the world's most important bilateral relationships.

Xi's comments came hours after China's military chief bluntly criticized the United States for holding military exercises in the South China Sea and conducting surveillance flights off its shores.

General Chen Bingde, speaking alongside Mullen, said recent U.S. exercises with the Philippines and Vietnam are “extremely inappropriate” at a time when China is embroiled in tense territorial disputes with both countries. He later said U.S. spy planes are flying within 25 kilometers of China's borders. He urged the United States to consider the feelings of the Chinese people.

Mullen, who is in China on a four-day visit, responded that the United States has been staging drills with its friends and allies in the region for decades and will continue to do so. He said the United States will also continue the surveillance flights, which are within “international norms.”

Chen also said the U.S. is spending too much on its military and, asked if, given the effects of the financial crisis over the past few years, that was “putting too much pressure” on American taxpayers.

Chen told the official Xinhua news agency that apart from the South China Sea disputes, the two had discussed cyber security, China's military development and the attitude of some U.S. politicians toward China.

Mullen's visit to China is the first by a U.S. military chief of staff since 2007. He is returning a visit by Chen to the United States in May.

Mullen said after his arrival in Beijing Sunday that he is worried that China's disputes with the Philippines and Vietnam could spin out of control. The countries have competing claims to parts of the South China Sea believed to be rich in oil and gas.

China says the United States should stay out of the disputes, but Washington has reaffirmed its commitment to a mutual defense treaty with the Philippines. The United States has also declared a national interest in maintaining free navigation through the waterway, which carries vital sea traffic between Northeast Asia, and Europe and the Middle East.