NEW: U.S. State Department confirms four Americans were killed in last week's attacks
Police corral several hundred anti-immigrant protesters at a memorial site
Nine people were taken in for questioning Sunday after raids, prosecutor's office says
Protesters interrupted a memorial gathering for Brussels attack victims Sunday, raising their arms in Nazi salutes and shouting anti-immigrant slogans as they scuffled with people who’d gathered for a peaceful vigil there.
Organizers had postponed a scheduled march in Brussels out of security fears, but some mourners gathered at the Place de la Bourse in a commercial district of the Belgian capital to create a makeshift memorial Sunday. They laid flowers at the foot of the stairs leading to the Brussels Stock Exchange.