Final answer:
The Department of Justice, through its Antitrust Division, oversees antitrust enforcement in international commerce, ensuring competitive practices in the marketplace.
Step-by-step explanation:
The U.S. government agency responsible for antitrust enforcement in international commerce is the Department of Justice, specifically its Antitrust Division. The Antitrust Division works to promote and protect free and fair competition in the marketplace, including international commerce. Its responsibilities include preventing anticompetitive mergers, prosecuting cartels, and overseeing antitrust enforcement in general. This includes prohibiting firms from agreeing to fix prices, rigging bids, or sharing or dividing markets.