Prosecutors raided the minor opposition Unified Progressive Party (UPP) over allegations of a rigged primary, an official said Monday, amid deepening factional infighting over how to revive the left-wing party.

Prosecutors came to the party's headquarters in southeastern Seoul with a warrant, said Lee Jeong-mi, a party spokeswoman.

A senior party official and a lawyer were believed to be checking the details of the warrant.

The raid came about three weeks after a civic group brought an accusation of primary election fraud to the prosecutors.

Earlier this month, the party announced after a two-week internal investigation that the primary designed to select its proportional representation candidates for the April 11 elections was rigged. (Yonhap News)