Brazilian federal police have arrested the treasurer of Brazil's ruling Workers Party in a wide-ranging investigation into corruption at state-run oil giant Petrobras, with the party saying later that he has offered to resign.

Joao Vaccari Neto was arrested on Wednesday in Sao Paulo as he was heading out for an early morning jog, police and judicial officials said in the southern city of Curitiba, where the investigation is centered.

An arrest warrant also was issued for Vaccari's sister-in-law, while his wife was questioned in connection with a series of unidentified deposits in her account that investigators suspect might be related to a kickback scheme at Petrobras.

Vaccari has maintained his innocence, telling a congressional panel last week that all the donations made to his party during last year's campaign were perfectly legal.

Rui Falcao, the Workers' Party president, said in a statement posted on the party's website that "for practical and legal matters Vaccari asked to step down as the party's treasurer".

But Falcao also called Vaccari's arrest unnecessary and expressed confidence in his innocence.

"We reaffirm our confidence in Joao Vaccari's innocence not only because of his conduct as treasurer, but also because in a democracy everyone is innocent until proven guilty," his statement said.

"The party is confident that in the end truth will prevail."

A member of the Workers' Party later called an emergency meeting to discuss Vaccari's arrest.

Under investigation

More than 100 people have been charged in connection with the Petrobras case, and more than 50 politicians are under investigation.

Among those are two former chiefs of staff to President Dilma Rousseff, but Vaccari is the seen as the closest figure to Rousseff so far to be implicated in the scandal.

Rousseff herself, who served as chairwoman of the board at Petrobras during a period when the alleged the graft took place, has not been implicated.

Vaccari was charged last month with corruption and money laundering in connection with the scheme, which prosecutors have described as the biggest ever uncovered in Brazil.

According to federal prosecutors, big construction and engineering firms paid at least $800m in bribes and other funds in return for inflated contracts with Petrobras, which is Brazil's biggest company.

Part of that money allegedly went to the Workers Party and other parties for political campaigns.

Igor Romario de Paula, a federal police officer, said on Wednesday that officials had been collecting evidence against Vaccari "for a long time".

He said the judge in the case, Sergio Moro, decided to order Vaccari's detention due to his "criminal habits, recidivism, a clear danger to public order and because of the kind of projection he has, the influence of the job he has today and the possibility of his fleeing".

Brazilian law sets no limit to how long those under preventative arrest can be detained.

Source: AP