Brazilian President Dilma Rousseff faced the biggest challenge yet of her young and turbulent second term, as hundreds of thousands of protesters took to streets in more than 150 cities to demand her impeachment and an end to corruption.

The Sunday protests, organized by right-leaning groups on social media and held across the continent-sized nation, had none of the violence seen in massive anti-government demonstrations that hit the country in 2013 and lingered into the following year.

They add to the mounting pressure on Rousseff, who is facing both political and economic crises as Brazil's economy stalls and dozens of top political figures are investigated in a kickback scheme at state-run oil company Petrobras, which prosecutors label as the largest graft scheme yet uncovered in the country.

The biggest protest was seen in Sao Paulo, where some 210,000 people gathered on a main avenue, according to the polling and statistics firm Datafolha. Large gatherings were also seen in the capital Brasilia, Rio de Janeiro and the southern city of Porto Alegre.

Rousseff didn't appear in public, but government ministers held a nationally televised press conference in which they said they would introduce anti-corruption measures in Congress, action the president promised during her campaign for re-election in October.

"We are here to express our indignation with the government-sponsored corruption and thieving, and to demand Dilma's impeachment," said Andre Menezes, 35, protesting on Avenida Paulista in Sao Paulo.

"She may have not been directly involved in the corruption at Petrobras, but she certainly knew about it, and for me that makes her just as guilty and justifies her ouster," he added.

In Rio, police estimated 15,000 people marched along the golden sands of Copacabana beach, where they waved Brazilian flags and many openly called for a military coup to dissolve the government.

In contrast to the widespread violence seen during Brazil's 2013 protests, on Sunday the only conflict reported was police using tear gas and stun grenades to disperse a small group of protesters in Brasilia who authorities said were trying to enter the Congress. In Sao Paulo, police arrested about 20 young men who were carrying powerful fireworks and brass knuckles.

Justice Minister Jose Eduardo Cardozo defended the government, emphasizing Rousseff's record as a leftist guerrilla who stood up to Brazil's 1964-85 military regime — and who was jailed for three years and brutally tortured because of it.

Rousseff has said she fully supports peaceful demonstrations and Cardozo added Sunday night that the rallies "confirm that Brazil is a democratic state that allows for divergences, the existence of opposing opinions and that we're far from any coup option."

Much protester ire was focused on a kickback scheme at Petrobras, in which at least $800 million was paid in bribes and other funds by Brazil's biggest construction and engineering firms in exchange for inflated Petrobras contracts.

Top executives are already in jail and the attorney general is investigating dozens of congressmen, along with current and former members of the executive branch, for alleged connections to the scheme that apparently began in 1997 before Rousseff's party took power in 2003. Rousseff, a former chairwoman of Petrobras' board, has not been implicated and so far is not being investigated, though top officials from her administration, including two former chiefs of staff, are caught up in the inquiry.

The mass marches are another thorn in Rousseff's side, adding impetus to opposition efforts to thwart measures she backs in Congress.

Brazilian growth has been weak since Rousseff took office in 2011. The country likely entered a recession in 2014 and most economists surveyed by the Central Bank forecast negative growth this year. Inflation is rising and the currency has plummeted against the dollar in recent weeks, making life more expensive in a nation with a surprisingly high cost of living.

Still, Brazil's top opposition political figures say impeachment is undesirable, because the president isn't accused of any connection to the Petrobras scandal, and because it could affect Brazil's stability.

Pedro Arruda, a political scientist at Sao Paulo's Pontifical Catholic University, said demonstrators have the right to demand Rousseff's ouster, "but the impeachment they ... demand has no legal foot to stand on."

At Copacabana, protester Sheila Alcantara said she recently had to close a restaurant she owned because of rapidly rising prices for electricity and food. "Never in my life have I heard of so much corruption, of so much money lost."

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Brooks reported from Rio de Janeiro and Lehman from Sao Paulo. Associated Press writer Adriana Gomez Licon contributed from Rio de Janeiro.

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