Plainclothes federal agents detained at least four people Tuesday morning in what were believed to be among the first arrests of undocumented immigrants at San Francisco Immigration Court, according to attorneys and advocates.

A reporter from The Standard witnessed several plainclothes federal agents — one with an ICE badge around his neck — walk a man in handcuffs out of 100 Montgomery St. and load him into a white van with Department of Homeland Security plates. Immigration attorneys and advocates said they witnessed three additional arrests.

The federal agents declined to answer questions when approached.

A Chevrolet Impala, parked on the street, was accompanied by a uniformed officer. A paper sign on the dashboard read “ICE Official Business.”