More than 200,000 activists rallied across the US on Tuesday, demanding an overhaul of immigration laws and greater rights for the country's estimated 12 million illegal workers.
Overwhelmingly peaceful May Day protests were held in more than 20 cities -- including Los Angeles, Chicago, Detroit and New York -- by a broad coalition of immigrant rights' campaigners.
The rallies took place on the one-year anniversary of massive nationwide protests which saw more than one million mostly Hispanic workers stage an "economic boycott" by skipping work for a day.
Divisions among activist groups about the best way to campaign for reform as well as fear among illegal workers following a series of immigration crackdowns led to a lower turnout, activists say.
But in Chicago, many protesters said they were motivated by a high-profile raid by heavily armed FBI agents in the heart of one of the largest Mexican neighborhoods in the Midwest.
Police put the size of the demonstration at around 150,000, while organizers claimed 1 million protesters marched through the heart of the city waving US flags, wearing white T-shirts and chanting "si, se puede" (yes we can).
A steady stream of protesters poured into the city's downtown Grant Park, where they were greeted by the city's powerful Democratic Mayor Richard Daley, who castigated federal politicians for failing to pass substantive immigration reform.
"Will you please stop dividing our families," Daley told the cheering crowd.
"Our nation is one of compassion and understanding and we have to understand this country was built by immigrants past, present and future," he said.
In Los Angeles, where around 500,000 protesters brought the city's business district to a halt last year, police said between 8,000 to 10,000 people had gathered for a march to city hall.
At a second march in Los Angeles, riot police clashed with some protesters, firing rubber bullets and tear gas, police said. A spokesman said police responded when objects were thrown at and struck about 15 officers. At least one person was arrested, a police spokesman said.
Waving US and Mexican flags, marchers called for reform to offer a route to citizenship for illegal immigrants. Many carried placards reading "Legalization Now!" and chanted "Stop the deportations."
Flavia Jimenez, an analyst at the National Council of La Raza, the largest non-profit Latino rights organization in the US, said workers were wary of possible repercussions if they protested.
The Los Angeles protests forced the closure of 17 downtown streets and altered some 60 bus routes.
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