A Supreme Court official said Senator Delcidio do Amaral, the leader of President Dilma Rousseff's Workers' Party in the upper house, was detained in Brasilia on Wednesday.

The veteran politician is one of several under investigation for allegedly taking bribes in the massive kickback scandal at state-run oil giant Petrobras, but he is the first to be arrested.

Also on Wednesday, federal police arrested billionaire investment banker André Esteves in Rio de Janeiro for allegedly obstructing the investigation into the scandal. The CEO of investment bank BTG Pactual is estimated by "Forbes" magazine to have personal wealth amounting to $2.2 billion (around 2 billion euros).

Interfered in probe

Under Brazilian law, the Supreme Court must approve any arrest of sitting members of parliament. The court's justice, Teori Zavascki, said he gave police permission to act after he was presented with evidence suggesting Amaral had obstructed the corruption investigation.

Search warrants were also issued for the senator's home in Mato Grasso, and his office in Brasilia.

Prosecutors said Amaral was recorded telling the son of former Petrobras international director Nestor Cervero that he shouldn't cooperate with authorities. He also allegedly offered to help Cervero flee the country in return for his silence.

Cervero was sentenced in August to 12 years in jail for corruption and money laundering in connection to bribes paid to acquire an oil refinery in Pasadena in the US state of Texas. Police allege Cervero passed bribe money to Amaral.

Workers' Party under fire

Petrobras - Brazil's largest company by turnover and market capitalization, which is more than 60-percent state-owned - estimates it lost more than $2 billion in the graft scheme dating back to at least 2004. Prosecutors say construction and engineering firms paid at least $800 million in bribes in exchange for lucrative Petrobras contracts. The excess funds were then funneled into the coffers of executives, politicians and parties, including the ruling Workers' Party.

President Rousseff, who was chairwoman of the Petrobras board from 2003 until 2010, has denied knowledge of wrongdoing and urged a thorough investigation. Although she had not been named in the probe, her governing party has come under increasing pressure.

Since an investigation was launched in March 2014, dozens of politicians and business directors have been accused of financial crimes including corruption and money laundering.

nm/msh (AFP, Reuters, dpa)