SEOUL - South Korean police privately investigated Prime Minister Han Duck-soo over President Yoon Suk-yeol's martial law imposition, Yonhap news agency said Friday.

The National Office of Investigation (NOI) conducted a face-to-face investigation in private into Han, who was serving as the acting president following Yoon's impeachment, as a suspect over the case of an emergency martial law that was imposed by Yoon on the night of Dec 3 but was revoked by the National Assembly hours later.

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The NOI questioned nine cabinet members as a suspect or a witness who participated in the cabinet meeting held right before the martial law declaration.

Among the total of 12 joining the cabinet meeting, the impeached president, the arrested defense minister and the unification minister were excluded from the NOI questioning.

Police were considering the second summons among the cabinet members.

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Yoon was named by investigative agencies as a suspect in insurrection and other charges.

The impeachment motion against Yoon was passed by the National Assembly on Dec 14 and delivered to the constitutional court to deliberate it for up to 180 days, during which Yoon's presidential power is suspended.