The Supreme Court on Thursday upheld a lower court ruling that cleared the country's first female prime minister of bribery charges.

Han Myeong-sook, who was prime minister between 2006 and 2007 under the late liberal President Roh Moo-hyun, was found not guilty of taking US$50,000 in bribes while in office from former Korea Express chief executive Kwak Young-wook.

"Kwak's testimony lacks objectivity and rationality," the court said in its ruling, adding that it is difficult to rule out the possibility that Kwak could have made false statements to prosecutors.

In 2009, prosecutors indicted Han, arguing that she took the kickbacks during an official luncheon held at the prime minister's residence in central Seoul in December 2006, in return for helping Kwak land the top position at a state-run corporation.

A Seoul district court, however, acquitted Han of the bribery charges in October, 2011. A Seoul appellate court in January of last year upheld the lower court's ruling, saying that the testimony of Kwak lacks credibility and consistency.

Kwak, in the same Thursday ruling, received a confirmed two-and-half-years prison term, suspended for four years, for embezzling funds from Korea Express.

Thursday's ruling helped Han put behind her one of two major bribery cases, with a second criminal case awaiting the appellate court's decision.

The Seoul Central District Court cleared Han on separate charges of taking nearly 900 million won (US$784,313) as political funds from Han Man-ho, the head of a local construction company, in violation of the Political Fund Law.

Han, who is currently a lawmaker with the main opposition Democratic United Party, stepped down from the chairwoman post last year to take responsibility for the party's defeat in the April 11 parliamentary elections. (Yonhap News)