A relative state of calm in Los Angeles began to crumble early Sunday afternoon as demonstrators confronted federal authorities guarding a downtown detention facility where chaos erupted as National Guard soldiers deployed tear gas on an increasingly agitated crowd.

U.S. officials said about 1,000 National Guard members were in the city under federal orders by midday Monday.

As protests in Los Angeles entered its fourth day, the federal government escalated its tense standoff with California as it prepared to send in 700 marines.