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Police in Brussels surrounded a group of demonstrators about 400-strong who descended Sunday on a memorial for those killed in terror attacks earlier in the week.

Some of the marchers were thought to be a part of the right-wing group "The Nation." They carried anti-ISIS and anti-terror signs and chanted as they made their way to the Brussels Stock Exchange, where they were met with police in riot gear. Twelve of the protesters were arrested after explosive objects were thrown at the officers, according to a spokesman for the Brussels Police.

The police fired a water canon at the group at least once — as crowds who were originally there to hold a peace rally in the Place de la Bourse cheered. A remembrance ceremony scheduled for Sunday afternoon was canceled Saturday by Brussels authorities citing the level 3 terror threat. But people gathered in the square outside of the iconic stock exchange building anyway.

As the right-wing protesters were pushed back by officers, they shouted: "This is our home." Most were clad in black, while some were masked.

Cheers later rang out as members of the peaceful group were able to string a banner of more than a dozen nations’ flags tied together across the length of the steps outside the stock exchange building.

Shortly after the flags were hoisted, at about 4 p.m. local time (10 a.m. ET), relative calm was reestablished in the square.