LJUBLJANA, Slovenia (AP) — Slovenia's main opposition leader was among five people briefly detained Thursday in an alleged multimillion-dollar corruption investigation into the building of a sports complex, investigators said.

Police searched Zoran Jankovic's house and his office in the capital, Ljubliana, where he is also mayor. His son, Jure Jankovic, a businessman, was also detained.

Robert Crepinko, head of the National Bureau of Investigation, said police searched 23 homes in Slovenia in the probe into suspected irregularities with the sports hall in Ljubljana.

"The focus of the investigation is financial transactions worth more than €10 million ($12.8 million)," he said.

Crepinko gave no other details.

Media in Slovenia reported that Jankovic is suspected of abuse of office and of siphoning city funds to companies with ties to himself and his family.

Jankovic resumed his mayor duties later Thursday after he was released from detention.

"Policemen who came this morning behaved correctly and in the city hall they took some documents," Jankovic told reporters.

He has dismissed previous allegations of corruption, claiming they were politically motivated.

Jankovic and his center-left Positive Slovenia coalition won the most votes in a parliamentary election last December. But he failed to form a government and a center-right coalition led by current Prime Minister Janez Jansa took power.

The two men are longtime rivals.

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Dusan Stojanovic and Jovana Gec contributed from Belgrade, Serbia.