US stock futures were lower after chip darling Nvidia warned of a $5.5 bln charge linked to a U.S. export ban on some chips.

(Reuters) -Wall Street index futures dropped on Wednesday and chip darling Nvidia slumped after the company flagged steep charges from new U.S. curbs on chip exports to China, fuelling worries about the fallout of an escalating trade war.

Shares in Nvidia slumped in after-hours trading late Tuesday after it said that tighter U.S. government controls on its exports of computer chips used for artificial intelligence will cost it an extra $5.