Traffic in parts of downtown L.A. were jammed because of a demonstration by critics of Arizona's new law cracking down on illegal immigrants.

The LAPD said some of the protesters were blocking several streets, including Alameda and Commercial streets. KTLA News video showed police making arrests of demonstrators lying in the street.

Traffic at the civic center near L.A. City Hall was backed up.

The protest was outside the federal prison in downtown L.A. "This detention center symbolizes the incarceration and internment of so many immigrants and the separation of families," according to a statement on a website posted by the protesters.

Officials said the protest could cause traffic problems for several hours and might cause disruption for people trying to drive into the detention facility parking lot.

KTLA News video showed gridlock on some streets as motorists struggled through detours.