SEOUL -- South Korea's parliament on Thursday voted for the appointment of three constitutional court justices to fill vacancies on the nine-member bench for President Yoon Suk-yeol's impeachment trial over his martial law imposition.

Two justices were nominated by the main liberal opposition Democratic Party, and one was nominated by the ruling conservative People Power Party, most of whose lawmakers boycotted the vote.

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

Yoon, who was named by investigative agencies as a suspect on insurrection charge, declared an emergency martial law on the night of Dec 3, but it was revoked by the National Assembly hours later.

To oust Yoon from office, at least six out of nine constitutional court justices are required to uphold the impeachment motion.

Of nine justices, three are nominated by the National Assembly, three by the president and three by chief justice of the Supreme Court.

The appointment of the three justices, which was passed in the opposition-controlled National Assembly, needs to be ceremonially approved by the president.

Prime Minister Han Duck-soo, who became an acting president following Yoon's impeachment, officially refused to approve the appointment, saying in an address earlier in the day that he will delay the approval until the ruling and opposition parties reach an agreement.

The Democratic Party said it will table an impeachment motion against Han and report it to the National Assembly later in the day, planning to vote on the motion Friday.