Just days before the Senate seemed near-certain to suspend Rousseff for six months and open an impeachment trial, the new leader of the lower house threw a spanner in the works dramatically ramping up the instability gripping Latin America's biggest country.

Waldir Maranhao, the interim speaker, ordered that a new vote in the lower house should take place on whether to impeach Rousseff in the coming days, following five official sessions in the chamber.

The cancellation of the lower house vote was ordered in response to a request by Rousseff's solicitor general, who had challenged its legitimacy.

Maranhao said the original vote by lower house deputies had "prejudged" Rousseff and denied her "the right to a full defense."

However, it was not immediately clear how the chaotic new development would play out.

The Senate had been due to start its own voting process on Wednesday, with a majority expected to back suspension of Rousseff. Once suspended, she would face a trial lasting months, with a two-thirds majority needed eventually to eject her from office.

Early signs were that the Senate would ignore Maranhao's order, possibly prompting a decisive battle in the Supreme Court.

The head of the chamber's impeachment committee, Raimundo Lira, said that the vote would go ahead as planned, regardless of Maranhao's intervention.

However there was no immediate word from the powerful Senate president, Renan Calheiros, who was reported to be meeting with party leaders.

A delighted-looking Rousseff interrupted a speech to supporters to say that she'd just got unconfirmed news of the impeachment drive hitting a roadblock.

"I don't know the consequences. Please be cautious," she said, calling on her backers to "defend democracy."

The impeachment battle has taken so many unexpected twists that Brazilians refer to it as a real-life version of the Netflix political drama "House of Cards."

Rousseff, from the leftist Workers' Party, is accused of illegally manipulating government budget accounts during her 2014 re-election battle to mask the seriousness of economic problems. But she says the process has been twisted into a coup by right-wingers in the second year of her second term.

Her removal had been looking increasingly certain after the lower house voted in mid-April by an overwhelming majority to send her case to the Senate for trial.

In the Senate, around 50 of the 81 senators have said they planned to vote in favor of an impeachment trial, well over the simple majority needed to open the process. The vote result had been expected on Thursday, followed shortly afterwards by Rousseff's departure from the presidential offices. Ministers have reportedly already been clearing their desks.

Adding to the confusion, Maranhao, the man at the center of the latest episode, is little-known to most Brazilians.

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