CURITIBA, Brazil – Former Brazilian President Luiz Inacio Lula da Silva arrived Saturday night at the headquarters of the Federal Police in Curitiba as he began a 12-year prison sentence for corruption.

Lula, who was convicted last July and had his sentence increased to 12 years and one month from 10 years on appeal earlier this year, was flown to Curitiba from Sao Paulo after turning himself in to authorities in compliance with the jail sentence issued on Thursday.

Riot police stationed outside the police headquarters used tear gas as they tried to disperse a large crowd of Lula sympathizers and detractors. Nine people were injured in the unrest, police said.

Hundreds of his supporters had blocked the entrance to the headquarters of the Metalworkers Union, where Lula had been staying, in an attempt to prevent him from turning himself in to police.

The former union leader was sentenced for accepting bribes in exchange for helping Brazilian construction company OAS obtain lucrative contracts from state oil company Petrobras.

Lula vehemently maintains his innocence, arguing that the accusations against him are aimed at preventing him from running in October’s presidential election, for which he is leading the polls.

Sergio Moro, the judge who handed down the original corruption conviction against Lula, issued a decree late Thursday giving the former head of state until 5:00 pm Friday to surrender to Federal Police in Curitiba, a city in southern Brazil.

Lula did not meet that deadline, but told his supporters earlier on Saturday that he would comply with the order.