PRAGUE—Czech Prime Minister Petr Necas, who has made rooting out public corruption one of his rallying cries, came under mounting pressure to resign Friday after his chief of staff and six other public officials were charged with alleged bribery or abuse of power.

Prosecutors said more people could still be charged following searches of 31 locations Thursday by more than 400 police officers, who impounded large quantities of documents, up to 150 million koruna ($8 million) in bank notes and tens of kilograms of gold.

The prime minister's chief of staff, Jana Nagyova, was the only person identified by prosecutors among the seven charged. She was accused of abusing public office through the unsanctioned use of military intelligence, said chief state prosecutor Ivo Istvan.

The other six people were facing either the same abuse of office charge or one of allegedly bribing former Czech lawmakers, he said.

"The circumstances of who knew about these actions, or possibly if they participated, continues to be a subject of investigation," he said. "We are looking into all leads."