RIO DE JANEIRO : Brazil's leftist President Dilma Rousseff huddled with cabinet ministers Monday after mass demonstrations calling for her resignation pushed Latin America's biggest country further into crisis.

Rousseff made no comment after her meeting in the capital Brasilia, but in the wake of Sunday's protests, she is fighting for her political life.

Between one and three million people flooded the streets of Sao Paulo, Rio, Brasilia and some 400 other cities, according to conflicting data.

Turnout in Sao Paulo was estimated at 500,000 by the research center Datafolha and 1.4 million by the Sao Paulo military police. The figures surpassed estimates by either organization in previous opposition demonstrations. Protesters said they were fed up with the country's worst recession in 25 years, a massive corruption scandal unfolding at state oil company Petrobras and the government's complete inability to pass laws in Congress.

The historic rebuff on the streets left Rousseff few options as another grueling week started, with Congress geared up to relaunch stalled impeachment proceedings.

An attempt to impeach the country's first female president began last year but fizzled out on technicalities. On Wednesday or Thursday, the Supreme Court is expected to set out the rules, opening the door for Rousseff's many enemies in the legislature to ramp up the pressure.

In parallel to the political assault against Rousseff, her mentor and predecessor as president, Luiz Inacio Lula da Silva, faces money laundering charges related to the Petrobras probe.

Prosecutors indicate that his legal troubles are only just beginning, and there has been a request to a judge that he be put into preventative detention.

For Rousseff, this threatens a key ally. Lula, who founded the ruling Workers' Party and was president from 2003-2010, is far more popular than Rousseff and gives her much of her credibility with the left-wing base.

Lula, who denies charges that he failed to declare ownership of a luxury seaside apartment, defiantly says that prosecutors have only spurred him into deciding on a comeback attempt as president when Rousseff's second term ends in 2018.

"I am an old man who was trying to rest," Lula, 70, told police 10 days ago when he was briefly detained for questioning in the Petrobras probe.

"I will be a candidate for the presidency in 2018, because I think a lot of the people who've been on my back will be getting the same treatment from me from now on," he said, according to a transcript released Monday.

Planning the next election may be premature with Rousseff battling just to survive her second term.

The impeachment case rests on allegations that Rousseff's government illegally manipulated accounts to boost public spending during her 2014 re-election campaign.

During the first push last year, analysts reckoned that Rousseff could still get enough votes from sympathetic deputies to survive. That is becoming less clear.

Her Workers' Party is in a shaky coalition with the bigger PMDB. On Saturday, a PMDB congress discussed pulling out altogether, with a decision to be taken in 30 days.

Relations between the Workers' Party and the PMDB have been strained for a long time. But the PMDB leader Michel Temer is Rousseff's vice president and as such would replace her automatically should she be impeached - a tempting incentive for the biggest party in Congress.

Analysts said all parties were watching the protest turnout on Sunday and that the big crowds could help push wavering deputies to support impeachment.

"This has been a very bad weekend for the government," said analyst Sergio Praca at the Getulio Vargas Foundation in Rio. "The demonstrations were very powerful... It's the worst scenario possible for the government."

However, another political analyst at the same foundation, Michael Freitas Mohallem, said that Rousseff could still make the numbers work.

"She only needs one third of Congress plus one, or 172 votes, to survive and that should not be very difficult," he told AFP.

An indicator of how much support the Workers' Party can still muster will come this Friday when Rousseff supporters plan their own street protests.