The arrest of the high-profile treasurer of Brazil's governing party has brought the unfolding corruption scandal at the country's state-owned oil company uncomfortably close to President Dilma Rousseff, analysts said Thursday.

It could also intensify calls for the impeachment of Rousseff, who has always denied any knowledge of the kickback scheme at Petrobras but was targeted by huge protests across Brazil on Sunday decrying corruption.

According to federal prosecutors, big construction and engineering firms paid at least $800 million in bribes and other funds in return for inflated contracts with Petrobras, which is Brazil's biggest company. Part of that money allegedly went to the governing Workers Party and other parties for political campaigns.

Joao Vaccari Neto, the party treasurer who was arrested Wednesday, has been charged with corruption and money laundering in connection with the scheme.

Ricardo Ismael, a political scientist at Rio de Janeiro's Pontifical Catholic University, said Vaccari's arrest is a problem for Rousseff, "whose campaign involved large sums of money that he was in charge of obtaining."

Vaccari is the highest-ranking member of the Workers' Party yet arrested for alleged involvement in the scandal and "the question that arises with his arrest is if other party leaders knew of the scheme and were involved in it," Ismael said.

The analyst said Vaccari's arrest also could bring the scandal close to Rousseff's predecessor and mentor, Luiz Inacio Lula da Silva, who has not been implicated in the scandal.

"He is very close to the former president and has had close ties with him for many years," Ismael said.

Hours after Vaccari's arrest, Workers' Party President Rui Falcao posted a message on the party's website saying Vaccari had stepped down as party treasurer. But Falcao called Vaccari's arrest unnecessary and expressed confidence in his innocence.

Vaccari has maintained his innocence, telling a congressional panel last week that all the donations made to the party during last year's campaign were legal.

More than 100 people have been charged in connection with the Petrobras case, and more than 50 politicians are under investigation. Among those are two former chiefs of staff to Rousseff, but Vaccari is seen as the closest figure to the president yet implicated in the scandal. Rousseff herself, who was chairwoman of Petrobras' board during several years as the graft took place, hasn't been implicated.

Alan Gripp, one of the editors of the newspaper O Globo, wrote that the "biggest impact of Vaccari's arrest is symbolic."

"The embarrassment of the arrest of the man responsible for irrigating campaigns of the Workers' Party will make the government bleed at a moment when it felt that its wounds (caused by the Petrobras scandal) were healing," Gripp said.

He wrote that the arrest will give members of the opposition ammunition for their demands that Rousseff be impeached. "There may be no legal arguments to sustain such a drastic measure, but so far it is the strongest argument the opposition has so far," he said.

Political commentator Eliane Cantanhede wrote in the newspaper O Estado de S. Paulo that "Vaccari's arrest is a dramatic event for the Workers' Party and Dilma, for it has enlarged the crisis."

"The impeachment thesis has gained strength and could lead to her resignation," Cantanhede wrote.

Opposition Sen. Jose Agripino agreed.

"Impeachment, which until recently was an idea that was avoided, is now the order of the day," he told reporters.