WASHINGTON (Reuters) - The U.S. Justice Department said on Tuesday that additional charges have been filed against a former IBM Corp software engineer in China, who was arrested in December by U.S. authorities for allegedly stealing proprietary source code from his former employer.

Jiaqiang Xu, 30, was charged in a six-count superseding indictment with economic espionage and theft of trade secrets, the department said in a statement. In December, he was charged with one count of theft of a trade secret, as prosecutors accused him of trying to sell the stolen code to other companies.

(Reporting by Eric Beech; Editing by Eric Walsh)