By Hyunsu Yim
SEOUL (Reuters) - South Korean police have questioned Prime Minister and Acting President Han Duck-soo as part of an investigation into the short-lived decision this month to impose martial law, an official at his office said on Friday.
The acting president was among 12 people present at a cabinet meeting on Dec. 3 shortly before President Yoon Suk Yeol's shock late-night announcement on martial law. Nine of those people have been questioned by a special police unit investigating the case, the Yonhap news agency reported.
Han, a career technocrat, became acting president after Yoon was impeached on Saturday following a parliamentary vote.
The official at Han's office did not say when he was questioned, but said it took place before Han was appointed acting president.
He was being investigated as a suspect, Yonhap reported.
Earlier this month, the main opposition Democratic Party reported Han to police after accusing him of insurrection.
Police officials were not immediately available for comment.
Han has previously said he had opposed the martial law declaration, which Yoon withdrew after barely six hours when outraged lawmakers rejected his decree.
Yoon faces a Constitutional Court trial on whether to remove him from office or restore his presidential powers following his impeachment.
He also faces investigations into whether the martial law declaration constituted insurrection, one of the few charges for which a South Korean president does not have immunity from.
A team of legal representatives and opposition lawmakers who will take on the role of prosecutors in the impeachment trial met on Friday.
"We gathered here today to fulfill our historical duty of impeaching Yoon Suk Yeol," said lawmaker Jung Chung-rae, who chairs the parliamentary legislation and judiciary committee leading the impeachment case.
The team includes a former Constitutional Court judge who was part of the panel that deliberated in the impeachment of former President Park Geun-hye.
The joint investigation team including police and the Corruption Investigation Office for High-ranking Officials summoned Yoon for a second time on Friday to appear for questioning on Dec. 25, Yonhap said.
Yoon did not respond to the first summons by the team earlier this week.
Police have tried unsuccessfully to raid Yoon's office to seek evidence after the presidential office security service denied them entry.
The opposition is scheduled to hold a confirmation hearing on new Constitutional Court judges next week that the ruling party has vowed to boycott.
South Korea's Constitutional Court currently has only six judges with three seats vacant.
Opposition parties and the ruling party have clashed over whether an acting president has the authority to appoint new judges to the court.
One judge was appointed to the court by an acting president previously during the impeachment of former President Park in 2017.