Thousands of women rallied Wednesday in support of President Dilma Rousseff, whose poll numbers have plummeted amid a national scandal involving state oil company Petrobras.

The beleaguered Brazilian leader addressed the gathering, vowing not to let the country go backwards, even amid difficult economic times.

Thirty-seven people were killed in three days in the Brazilian city of Manaus, and one hypothesis being considered is a coordinated wave of attacks involving police, an official said.

Evidence has emerged over suspects in some of the killings that occurred from Friday to Monday evening in Manaus, a river port in the middle of the Amazon rainforest, said Sergio Fontes, secretary of public safety in Amazonas state, the capital of which is Manaus.

Brazilian police investigating the giant Petrobras corruption scandal raided politicians, including former president Fernando Collor de Mello, in dozens of search and seizure operations Tuesday, prosecutors and local media said.

The raids, aimed at securing evidence before it could be destroyed or tampered with, took place across seven states in the latest expansion of a kickbacks and bribes probe centered on the state oil company.

Brazilian President Dilma Rousseff defied calls for her impeachment Tuesday, saying she would "not fall," despite rock-bottom ratings and mounting political troubles.

The unpopular leader, a one-time member of a leftist guerrilla group who was tortured during the military dictatorship ruling Brazil from 1964 to 1985, compared those calling for her to step down to "coup plotters."

Pope Francis celebrated an open-air mass with hundreds of thousands of faithful under scorching heat in Ecuador on Monday, highlighting the importance of family on his return to his home region.

The first pope from Latin America made an impassioned plea to fulfill the "social debt" toward families as he addressed some 800,000 people in a park in Guayaquil, Ecuador's largest city, according to official figures.

More than a million faithful -- some of whom traveled for hours and spent the night outdoors -- gathered Monday for the first open-air mass of Pope Francis's three-nation trip to South America.

Keeping vigil in tents, sleeping bags and on cardboard, tens of thousands hoping to catch a glimpse of the pontiff spent the night in the rough ahead of the service in Guayaquil, Ecuador's largest city.

Aside from listening in on Brazilian President Dilma Rousseff's phone calls, U.S. spies also targeted top political and financial officials, according to new information released by WikiLeaks on Saturday. 

The whistle-blowing website published a National Security Agency list of 29 Brazilian government phone numbers that the American spy group monitored.

The United States and Cuba have reached a deal to reopen embassies in Washington and Havana, in a major step toward ending decades of Cold War enmity.

President Barack Obama is expected to issue a statement at 11:00 am (1500 GMT) Wednesday in the White House Rose Garden about the deal, which constitutes one of the major foreign policy achievements of his presidency.

Brazilian President Dilma Rousseff said Tuesday she had confidence in her U.S. counterpart Barack Obama, laying to rest a scandal over U.S. intelligence monitoring of her telephone calls and those of millions of other Brazilians.

"Since then, some things have changed and the change is particularly due to the fact that President Obama and the U.S. government have stated on several occasions that they would no longer engage in intrusive acts of spying on friendly countries," Rousseff told a joint press conference. 

President Barack Obama and Brazil's Dilma Rousseff paid a surprise joint visit Monday to Washington's Martin Luther King Memorial, part of efforts to mend fences after a spying row.

Obama hosted the Brazilian president at the memorial to the civil rights icon -- one of his personal heroes --  after a "turbulent patch" between the two countries caused by revelations that U.S. spies had listened in on Rousseff's phone calls.