Brazil's Senate is pressing ahead with the impeachment process against President Dilma Rousseff despite a surprise decision by the lower house's interim speaker to annul it.

Renan Calheiros, the head of the Senate or upper house, said on Monday he had rejected the interim speaker's decision and that a vote in the Senate on whether to put Rousseff on trial would continue as scheduled.

"No monocrotic decision can super impose a collective decision, specially when the decision was taken with the highest form of collectiveness in the house," he said.

Earlier, Waldir Maranhao, who took over as acting speaker of the lower house last week, said there were procedural flaws in the April 17 vote in the chamber when it accepted the impeachment charges against Rousseff.

"I am aware that this is a delicate moment. A time at which we have the obligation to save democracy through debate. We are not, nor will we ever be playing with democracy," Maranhao said.

The previous speaker of the lower house, Eduardo Cunha, who orchestrated the impeachment process against Rousseff, was forced out by the Supreme Court last Thursday on charges of money laundering and corruption.

After that vote in the lower house, the impeachment process was passed to the Senate, where a committee recommended on Friday that Rousseff be put on trial by the full chamber for breaking budget laws.

Al Jazeera's Latin America Editor Lucia Newman, reporting from Brasilia, said protesters were out in front of Brazil's Congress once again, as the impeachment process took another extraordinary twist.

"It's a roller-coaster that Brazilians are hanging on for dear life," she said. "Nobody knows what's going to happen.

"Now not only the president is pitted against the legislator, but leaders of the upper and lower houses are in a war, neither one recognising the decision of the other.

"In the meantime, Brazilians are asking themselves just how long this political paralysis, driven by a political crisis that no one could have imagined, will last," Newman said.

Mark Weisbrot, co-director of the Center for Economic and Policy Research, told Al Jazeera that the Rousseff case exposed the flaws in Brazil's judiciary system.

"60 percent of the Congress is under some kind of scrutiny or investigation and when I think of all the major parties, the Worker Party, Dilma Rousseff's party is probably the least corrupt, although they had several corruption scandals within the Worker Party too," he said. "The whole system needs reform.

"It's kind of ironic because this is the government that finally gave the judiciary the power to investigate and then they abused it too and used it against this government."

The full Senate had been expected to vote to put Rousseff on trial on Wednesday, which would immediately suspend her from the president's job for the duration of a trial that could last six months.

During that period, Vice President Michel Temer was expected to replace Rousseff as acting president.

Raimundo Lira, head of the Senate's impeachment committee, has said the vote will go ahead as planned, regardless of Maranhao's intervention.

Before Calheiros overruled Maranhao's order, Rousseff interrupted a speech on Monday to supporters to say that she had just got unconfirmed news of the annulment order.

Brazilian markets fell sharply after the initial annulment of the impeachment process.