The US has told China it will not recognize an exclusion zone in the South China Sea, US Deputy Secretary of Defense Robert Work said on Wednesday.

US officials have expressed concern that an international court ruling expected in coming weeks on a case brought by the Philippines against China over its South China Sea claims could prompt Beijing to declare it an air defense identification zone, or ADIZ, as it did to the north, in the East China Sea, in 2013.

Work told an event hosted by The Washington Post that the US would not recognize such an exclusion zone in the South China Sea, just as it did not recognize the one in the East China Sea.

Meanwhile, China's defense minister asked Vietnam to deepen the countries' exchanges, communication, and friendship amid a festering territorial dispute in the South China Sea.

Chinese Defense Minister Chang Wanquan at a meeting with his South Korean counterpart at the Defense Ministry in Seoul on February 4. Reuters The two communist-led states' claims in the South China Sea came to a head in 2014, when Beijing parked an oil rig in waters off the Vietnamese coast, leading to anti-China riots.

Since then they have exchanged high-level visits, including a trip by Chinese President Xi Jinping to Hanoi last year.

Meeting Vietnam Communist Party chief Nguyen Phu Trong, Chinese Defense Minister Chang Wanquan said the two sides should strive to maintain the close ties forged in the past by leaders Mao Zedong and Ho Chi Minh.

The two militaries should "increase high-level exchanges and strategic communication, increase friendly feelings, deepen border defense exchanges and practical cooperation on UN peacekeeping, military academic research, and the defense industry," Chang said in a statement carried late Monday by China's Defense Ministry.

While there was no direct mention of the South China Sea, the ministry said the commander of China's South China Sea fleet, Shen Jinlong, attended the meeting.

Last month, tensions heightened between the two nations over territorial sovereignty in the South China Sea after Taiwan and US officials said Beijing had placed surface-to-air missiles on Woody Island, part of the Paracel archipelago that China controls.

File photo of Woody Island, part of the disputed islands in the South China Sea. Thomson Reuters

Vietnam called China's actions a serious infringement of its sovereignty over the Paracels.

China claims most of the South China Sea, through which about $5 trillion in ship-borne trade passes every year. Its Southeast Asian neighbors Brunei, Malaysia, the Philippines, and Vietnam also claim parts of the sea, as does Taiwan.

(Reporting by Ben Blanchard; Editing by Clarence Fernandez, Andrea Shalal)