South Korea's Constitutional Court ruled on Monday to strike down the impeachment motion against Prime Minister Han Duck-soo and restore his powers.

Han has already been reinstated as prime minister and acting president, as the ruling took immediate effect.

Of eight justices on the nine-member bench, five rejected the motion while one upheld it. The remaining two were in favor of dismissal.

The impeachment motion against Han was passed by the opposition-controlled National Assembly on December 27 last year following the impeachment of President Yoon Suk-yeol on December 14 over his botched martial law imposition.

Choi Sang-mok, the economy and finance minister who doubles as deputy prime minister for economic affairs, became acting president in December last year after the impeachments of both president and prime minister.

Despite confirmation that Han's impeachment process was legitimate, the court said neither evidence nor objective materials identified his involvement in impeached President Yoon Suk-yeol's martial law imposition and insurrection.

The court said Han's refusal to appoint constitutional court justices was unconstitutional, but it noted that evidence and objective materials failed to identify an intent to neutralize the ongoing deliberation on Yoon's impeachment.

Yoon declared emergency martial law on the night of December 3, but it was revoked by the National Assembly hours later.

(With input from agencies)