Romanian prosecutors said they detained President Traian Basescu's brother on Thursday on suspicions of ting a bribe to help keep an underworld boss out of jail, prompting the prime minister to call for the president's resignation.

Mircea Basescu was brought in for questioning after Florin Anghel, the son of crime boss Sandu Anghel, filed a criminal complaint against him. Anghel's father was sentenced to eight years and nine months in prison for almost fatally stabbing one of his nephews in a bar in 2011.

Florin Anghel released secret recordings to Romanian TV station Antena 3 on Wednesday that suggested Mircea Basescu had received cash from him for trying to sway magistrates to give Sandu Anghel a lighter sentence. They also suggested President Basescu had knowledge of his brother's dealings.

Anghel himself is under investigation for blackmail, prosecutors said.

Mircea Basescu has denied taking about $340,000 to influence the judiciary.

The leftist government of Prime Minister Victor Ponta told reporters President Basescu, who won his first term in 2004 on an anti-corruption ticket and has been a strong supporter of an independent judiciary, should step down.

"The president's resignation would be a natural gesture to eliminate any pressure on the judiciary," the prime minister's office said in a statement.

Earlier on Thursday, President Basescu strongly denied any involvement.

"There is suspicion that I was involved in the case," he told reporters. "This is why I am asking any policeman, prosecutor or judge who was involved in the sentencing of Sandu Anghel to say whether there was any intervention on my part.

"Being the president's brother does not exempt you from being subject to the law. Let me assure you that between the need to consolidate the judiciary and the natural impulse to defend one's brother, I choose consolidating the judiciary."

Romania ranks behind only Greece and Bulgaria in terms of corruption in the 28-nation European Union, according to Transparency International The European Commission has put Romania's justice system under special monitoring.

More than 1,000 people were convicted of corruption last year in the country. Those sent to trial included six Cabinet ministers and parliamentarians, five county council heads, 34 mayors and deputy mayors, judges, lawyers and managers of state-owned firms.