For the first time Beijing vowed to censure private companies involved in the arms sales to Taiwan by the United States, a measure seen as concrete by experts and demanded by Chinese netizens for a long time.

China said it would impose unspecified sanctions on the companies involved and reduce international cooperation with the US unless it canceled the new arms package. The foreign ministry didn't list the companies involved in its draft statement over the weekend.

But Sikorsky, Lockheed-Martin, Raytheon and Boeing, are four companies involved in the latest $6.4 billion sale. All four have so far declined to comment to the press.