Alphabet's Google needs strong measures imposed on it to prevent it from using its artificial intelligence products to extend its dominance in online search, a U.S. Department of Justice attorney said as a trial in the historic antitrust case began on Monday.

In the latest phase of the major antitrust trial that began on Monday, government lawyer David Dahlquist argued that Google has built a system where its control of search helps improve its AI products, which then send more users back to Google search, creating a cycle that keeps competitors locked out of both markets.