A 45-year-old man crashed an excavator into the South Korean prosecutors' office to protest the woman at the center of an influence-peddling scandal gripping the country's highest office.

The heavy vehicle smashed the gate and building of the Supreme Prosecutors' Office in Seoul and injured a security guard, police said.

The driver was arrested on site, police said.

The woman he was protesting against, Choi Soon-sil, was arrested on allegations she used her friendship with President Park Geun-hye to influence state affairs by gaining access to classified documents and benefited personally through non-profit foundations, officials said.

Choi was detained late yesterday, a prosecution official said, hours after she had arrived at the office of local prosecutors to answer questions.

Park is in the fourth year of a five-year term and the crisis threatens to complicate policymaking during the lame-duck period that typically sets in toward the end of South Korea's single-term presidency.