South Korea's opposition parties on Tuesday agreed to vote on extending the special investigation later this week if Acting President and Prime Minister Hwang Kyo-ahn fails to make the decision.

The decision came as an independent counsel, which is investigating the corruption scandal of President Park Geun-hye and her confidante Choi Soon-sil, must end its probe at the end of this month unless the acting president gives permission to extend the investigation by a month.

While opposition parties have been claiming that the acting president must give the approval, the ruling Liberty Korea Party has been protesting against the extension, apparently because prolonging the probe could have an adverse impact on the party's chances in the next presidential election, which may come as early as May.

Accordingly, representatives of the Democratic Party, People's Party, Bareun Party and Justice Party urged Hwang to arrive at a clear stance no later than the end of Tuesday.

"If Hwang fails to come up with his stance by Tuesday, the parliament will make full-fledged efforts to vote on revising the independent counsel law during the plenary session slated for Thursday," the party chiefs said in a joint statement.

The Liberty Korea Party, however, continued to protest against the extension of the special investigation.

"(The request) is a threat and a political attack aimed at gaining the upper hand at the presidential election," said Rep. Chung Woo-taik, the floor leader of the ruling party. "The call hides bad political intentions."

Chung claimed the independent counsel should faithfully conduct its probe until the deadline and let state prosecutors finish the investigation.

"Hwang should not be interrupted by the excessive demands made by the opposition party, and make a decision based on the law and principle," Chung added. (Yonhap)