Embattled Brazilian President Michel Temer has said he will fight allegations that he endorsed the paying of hush money to an ex-politician jailed for corruption.
Mr Temer spoke during a national address in his first appearance since the Globo newspaper published a report claiming he was recorded supporting payments to former lower house speaker Eduardo Cunha.
In his speech, Mr Temer categorically denied the allegation and insisted he will stay in his job.
Mr Temer took power a year ago when president Dilma Rousseff was impeached and then removed for illegally managing the federal budget.
"At no time did I authorise the paying of anyone," Mr Temer said emphatically, raising his voice and pounding his index finger against the podium.
"I did not buy anybody's silence.
"I will not resign."
Protests are planned in several cities and opposition politicians took to Twitter and local news channels to call for Mr Temer to be impeached, arguing his government no longer has legitimacy.
"I can't see how Temer survives this," said David Fleischer, a political science professor at the University of Brasilia. "There are just too many people against him now."
The ongoing scandal deepened at dawn on Thursday as police searched the Rio de Janeiro home and Brasilia office of Senator Aecio Neves, who nearly won the presidency in 2014 and planned to run again next year.
Mr Neves is being investigated in several corruption cases related to the "Car Wash" probe into kickbacks to politicians. He has denied any wrongdoing but the Supreme Federal Tribunal has suspended him from office indefinitely.
Within 90 minutes of opening, Brazil's main Ibovespa stock index dropped 10% and trading was stopped for 30 minutes.
Brazil's Real currency lost 8% of its value against the US dollar in the first half of Thursday. Both chambers of Congress cancelled sessions and Mr Temer's office axed his planned activities.
Globo reported late on Wednesday that Mr Neves had been recorded asking JBS meat-packing company executive Joesley Batista for 700,000 US dollars (£540,000) to pay for his "Car Wash" defence.
Globo also reported that Mr Batista had recorded Mr Temer endorsing a bribe to silence Cunha. In a statement late on Wednesday, the president's office said Mr Temer did not participate or authorise any attempt to keep Cunha from reaching a plea bargain with justice officials.
If confirmed, the allegations could prove devastating for Mr Temer, whose administration has lurched from one crisis to another since he took office just over a year ago.
Cunha led the impeachment fight that removed Ms Rousseff from the presidency last year and put Mr Temer, then the vice-president, into power. Cunha was later imprisoned on a 15-year sentence for corruption.
The statement from Mr Temer's office confirmed that the president did meet with Mr Batista in March. According to the Globo report, Mr Batista secretly recorded the conversations with Mr Temer and Mr Neves and gave them to justice officials as part of plea bargain negotiations.
The report said that when Mr Temer was told Cunha was being paid to keep silent, the president responded: "You have to keep that up, all right?"
Globo did not release the recordings or say how they were obtained.
Mr Temer and Cunha are members of the same party and were previously allies. However, they appear to have had a falling out amid a growing investigation into corruption involving the state oil giant Petrobras.
Since launching three years ago, the "Car Wash" probe into billions of dollars in kickbacks has put several top businessmen and politicians in jail.
Many believe that Cunha, who was widely viewed as Brazil's most powerful politician before being ensnared in several corruption cases, could provide damaging testimony about dozens of others if he reaches a plea bargain with investigators.