THE United States on Thursday blacklisted China's state-owned oil giant CNOOC over Beijing's increasing assertiveness in the South China Sea, and the tech firm Skyrizon for its ties to the Chinese Army. The US Department of Defence also added nine companies to its list Chinese organisations with military links, including smartphone maker Xiaomi and state-owned plane manufacturer COMAC.

The US government's announcement was a sign of the escalating tensions between the two giants, following four years of aggressive trade wars and diplomatic manoeuvres under President Mr Donald Trump.

The US Department of Commerce added China National Offshore Oil Corporation (CNOOC) Limited to the blacklisted entity list that forbids US firms from exporting or transferring technology with the companies names, unless permission is granted by the government.

CNOOC was targeted in "light of its role in the China's campaign of coercion against other claimants of an estimated USD 2.5 trillion in South China Sea oil and gas resources," said the State Department.

It stands accused of using its mammoth survey rig HD-981 off the Paracel islands in 2014 in an attempt to intimidate Vietnam. It has been involved in offshore drilling in the siputed waters of the South China Sea.

"China's reckless and belligerent actions in the South China Sea and its aggressive push to acquire sensitive intellectual property and technology for its militarisation efforts are a threat to US national security and the security of the international community," Commerce Secretary Mr Wilbur Ross said.

"CNOOC acts as a bully for the People's Liberation Army to intimidate China's neighbours, and the Chinese military continues to benefit from government civil-military fusion policies for malign purposes," he added.

The Treasury Department announced last week that it would add CNOOC to its sanctions list, freezing any assets under US jurisdiction.

Chinese state-owned Skyrizon was also added to the Military End-User (MEU) list for its capability to develop, produce, or maintain military items.

"Skyrizon-a Chinese state-owned company-and its push to acquire and indigenize foreign military technologies pose a significant threat to U.S. national security and foreign policy interests," said Mr Ross. "This action serves to warn the export community of Skyrizon's significant ties to the People's Liberation Army."

This means US firms will need a license to do business with the company.

The US administration hopes for investors to divest their stakes in the Chinese companies by November 2021, while S&P Dow Jones Indices has already de-listed several of them.