Workers Party Treasurer Joao Vaccari Neto (C) speaks as he testifies before a special committee of the Brazilian Congress, investigating alleged corruption in the state-owned oil company Petrobras, in Brasilia on April 9, 2015.

A hearing into a massive graft scandal at Brazil’s state oil firm #Petrobras was interrupted Thursday when a protester unleashed a mischief of mice on proceedings, sparking chaos at Congress.

Several mice were released by an unknown suspect in the middle of the hearing, interrupting a statement by ruling Workers Party treasurer Joao Vaccari Neto.

The small brown rodents created brief chaos among journalists and politicians attending the hearing as they scampered across the floor.

Security removed the person responsible for planting the mice, as onlookers said the hearing was being turned into a “circus.” The suspect was not named.

One lawmaker pointed his finger at a colleague and insisted he be reprimanded.

The rats released by an unhnown person during the hearing

“What happened must not go unpunished,” said Jorge Sola, accusing opposition lawmaker Waldir Soares de Oliveira of the Social Democracy Party.

“This must be recorded in the minutes,” Sola added.

De Oliveira denied any involvement.

Security officers removed the offending creatures and the proceedings resumed.

Vaccari is one of 27 people facing trial on corruption and money laundering charges relating to the graft scandal which broke 13 months ago.

He is accused of receiving millions in bribes as part of a multibillion-dollar kickback scheme embroiling some of Brazil’s top politicians.

Vaccari is one of the biggest names yet to fall under suspicion in a snowballing scandal that has rocked Brazil’s government. He allegedly received donations worth $1.2 million.

The scandal has wiped tens of billions of dollars off Petrobras’ market value and forced it to delay publishing externally audited accounts from last year. The company told AFP on Thursday it still did not have a definite date to release the accounts.

In January, Petrobras unveiled unaudited accounts showing profits down nine percent on the previous year.

Struggling to assess potential asset writedowns in the wake of the scandal, Petrobras indicated in its internal audit it had discovered 88.6 billion reais ($29 billion) of asset overvaluations but could not calculate losses stemming directly from the kickbacks affair.

Also Thursday, Energy Minister Eduardo Braga called for the amendment of legislation obliging Petrobras involvement in the extraction of all “pre-salt” oil deposits in the Atlantic under layers of salt.

Current legislation affords Petrobras sole operator status and a guaranteed 30 percent minimum share in pre-salt concessions.

But the graft scandal has hit the firm’s ability to raise investment, caused its share price to collapse and undermined its reputation as Brazil’s most prestigious company.

“The distribution regime needs to be revised … we cannot place such obligations on a company without the physical and financial capacity” to carry them out, Braga told a senate meeting.

Ruling Workers Party senator Delcidio Amaral said the current obligations placed on Petrobras did not make sense.

*AFP