The U.S. government's unprecedented use of National Guard troops in Los Angeles to protect officers carrying out President Donald Trump's immigration crackdown was illegal and should be ended, a lawyer for the state of California told a federal judge on Tuesday.

The three-day non-jury trial before San Francisco-based U.S. District Judge Charles Breyer will determine whether the government violated a 19th-century law that bars the military from civil law enforcement when Trump deployed the troops in June, as the state of California claims in its legal challenge.