Adds details from listings, background throughout

WASHINGTON, June 8 (Reuters) - The U.S. on Monday issued an updated list of Chinese firms that it believed to be aiding Beijing's military, including e-commerce group Alibaba 9988.HK, Internet search provider Baidu 9888.HK and automaker BYD 002594.SZ.

The Pentagon briefly posted an updated list in February but then took it down. The list released on Monday contains many of the firms that were added in February.

Other companies added include biotech firm WuXi AppTec 603259.SS and AI-driven robotics company RoboSense Technology Co Ltd 2498.HK.

Though the Pentagon list does not formally impose sanctions on Chinese firms, under a new law, the department will be prevented in coming years from contracting and procuring from companies on the list.

Being added to the list also sends a message to Pentagon suppliers and other U.S. government agencies about the U.S. military's opinion of the firms, some of which have sued the United States over their inclusion.