The minor opposition Unified Progressive Party (UPP) blocked prosecution officials for several hours on Monday from carrying out a raid on the party's headquarters over allegations of a rigged primary, an official said.

The standoff began Monday morning when prosecutors visited the party's headquarters in southeastern Seoul and submitted a warrant for the raid to look into the allegations.

Television footage showed several dozen party officials locked themselves inside a room in the party's headquarters as police and prosecution officials were standing outside the room's glass door.

Some 100 party officials were engaged in the standoff with eight prosecution officials in the party's headquarters, said Lee Jeong-mi, a spokeswoman of the party's emergency committee tasked with reforming the party following the primary fraud.

Some party officials posted slogans on the glass door that read "Prosecution, stop political oppression!" according to footage of news Y, Yonhap News Agency's all-news cable TV channel.

Two private companies, one which handled the computer program used in the primary, and another which manages the party's Web site and the party's members, also refused to allow prosecution officials to seize documents and computers, according to Lee.

The emergency committee chairman Kang Ki-kab urged the prosecution to stop its raid attempt as he vowed to reform the party mired in a crisis over factional infighting following the primary fraud.

Kang and other key party officials asked for a meeting with the top prosecutor by visiting the prosecutors' office in protest of the raid attempt, according to Lee.

Prosecutors were not immediately reached for comment.

The attempted 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.

The latest development comes amid deepening factional infighting over how to revive the left-wing party.

The party has called for the resignation of the 14 people who participated in the rigged primary to run for the April parliamentary elections as proportional representation candidates.

Six of the 14 candidates were elected as UPP lawmakers under the proportional representation system, which allocates seats to parties according to the numbers of votes they receive.

A female lawmaker-elect who ran in the primary has resigned and several other proportional representation candidates have also expressed their intention to step down.

On Friday, the emergency committee issued an ultimatum to two other lawmakers-elect accused of being involved in the rigged primary to step down by Monday morning.

However, Lee Seok-gi and Kim Jae-yeon, who were both convicted of engaging in pro-North Korean activities in the past, have refused to resign. The two have allegedly espoused North Korea's guiding "juche" philosophy of self-reliance and belong to the party's mainstream faction.

Meanwhile, the North's propaganda Web site Uriminzokkiri claimed that the U.S. has masterminded operations to accuse the UPP and other progressive forces of being pro-North Korean.

The Web site also said the South Korean equivalent of McCarthyism led by the U.S. is aimed at preventing South Korean progressive forces from advancing in the December presidential election, referring to anti-communist witch hunt in the U.S. in the 1950s.

President Lee Myung-bak's single five-year term ends in February 2013. He is barred by law from seeking re-election. (Yonhap)