SEOUL (Reuters) -South Korea's ousted former President Yoon Suk Yeol said on Saturday that he is leaving the conservative People Power Party (PPP), according to his Facebook post.

The announcement comes as PPP's presidential candidate is badly trailing liberal Democratic Party candidate Lee Jae-myung in the polls before the June 3 snap election.

According to a Gallup Korea poll released on Friday, some 29% supported PPP presidential candidate Kim Moon-soo, compared to 51% for frontrunner Lee.

Yoon, whose December surprise martial law and subsequent ouster by impeachment brought about the snap presidential election, had been called by party members to leave the party in an effort to muster more support from moderate voters who negatively view his actions.

"I am leaving the People Power Party to fulfill my responsibility to protect the free Republic of Korea ... Please lend your support to Kim Moon-soo," Yoon said in his post, referring to South Korea's official name.

Candidates Lee and Kim are set to face off in their first televised debate on Sunday.

(Reporting by Joyce Lee; Editing by Sandra Maler)