The militaries of the United States and China remain divided on serious issues such as US arms sales to Taiwan, US military reconnaissance activities off China's coast and disputes over the South China Sea.

Navy Admiral Mike Mullen, US chairman of the Joint Chiefs of Staff, made the remarks on July 25 during a press conference in Washington at the Foreign Press Center.

He said the two militaries took a "healthy step" in their relations as represented by the "candid" and extensive talks held between him and Chen Bingde, chief of the General Staff of the People's Liberation Army, in May during Chen's visit to the US and in mid-July during his visit to China.

However, he said it was difficult for the two militaries to “move past” their differences.

Talking about the US coming decision to sell arms to Taiwan, he argued that the US has "legal responsibility" to Taiwan, and he hoped the two militaries could “overcome the bumps” to sustain their exchanges.

It is reported that two Chinese fighter jets recently intercepted a US spy plane.

"We both have to be very careful... not to repeat what happened in 2001," he said.

He was referring to the incident in April 2001, during which a US military reconnaissance plane flew above waters off China's coast. China accused the US plane of violating flight rules. The incident caused the crash of a Chinese fighter plane and death of the Chinese pilot.

During the press conference, he also stressed that Asia-Pacific region is very important to US national security and the US will keep its commitment to the security in the region.