BRASÍLIA - The impeachment of Brazilian President Dilma Rousseff was thrown into confusion Monday when the speaker of the lower house of Congress annulled an April vote by lawmakers that launched the process.

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 by cancelling the vote that had got the entire process underway.

Waldir Maranhao, the interim speaker, wrote in an order seen by AFP that a new vote in the lower house should take place on whether to impeach Rousseff in five sessions time.

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

However, it was not immediately clear how the chaotic new developments would unfold and whether pro-impeachment leaders would appeal to the Supreme Court to try and keep the process going.

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.

In her first reaction, Rousseff interrupted a speech to supporters to say that she'd just got unconfirmed news of her impeachment 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 reelection battle to mask the seriousness of economic problems. But she says the process has been twisted into a coup by rightwingers 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 after 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.

He took the post of speaker only last week as replacement for Eduardo Cunha, the veteran speaker who was the architect of the controversial impeachment drive but was forced by the Supreme Court to stand down over corruption charges. Maranhao was to give a press conference at 4:00 pm (1900 GMT).

The political crisis comes on top of the deepest recession in decades in Latin America's biggest economy, just three months before it hosts the Olympic Games in Rio from August 5 to 21.

The affair has heightened tensions in the country which is in the midst of a giant corruption scandal involving state oil company Petrobras that has implicated numerous politicians including allies and enemies of Rousseff.

Rousseff has not been formally accused of corruption like many of her rivals. But prosecutors have called for her to be investigated for allegedly trying to obstruct a probe into the Petrobras affair.

Among the high-profile suspects are Cunha and her presidential predecessor Luiz Inacio Lula da Silva.

If Rousseff is suspended, she would be replaced by her vice-president-turned-enemy, Michel Temer.

Temer, a center-right leader, has been alleged to have been involved in the Petrobras affair but he has not been formally investigated. A Sao Paulo court has fined him for campaign financing irregularities and he could face an eight-year ban from seeking elected office.