South Korea's opposition parties on Monday urged the acting president to approve the extension of the independent investigation into a corruption scandal surrounding President Park Geun-hye.

The independent counsel must end its probe at the end of this month unless the acting president gives permission to extend the investigation by a month.

"Acting President and Prime Minister Hwang Kyo-ahn must remember if he does not approve the extension, he will face criticism that he blindly shields his companion," head of the Democratic Party Rep. Choo Mi-ae said, urging him to make a decision by Tuesday.

Hwang remained noncommittal later in the day when asked by reporters about the opposition party demand.

Choo also urged the Constitutional Court to conclude the hearings on Park's impeachment by Friday as planned to promptly come up with the final ruling and normalize state affairs paralyzed by the scandal.

The party head criticized Park's lawyers for requesting the Constitutional Court to delay proceedings.

"Such a shameless request is intended to drag on the impeachment trial indefinitely and damage the fairness of the Constitutional Court," Choo added.

The Bareun Party echoed the view, urging the Liberty Korea Party to make an official statement on the issue.

South Korea's four opposition parties agreed Sunday to seek a revision in the law to extend the deadline of the independent counsel if Hwang declines to give his approval.

The ruling party, on the other hand, claimed the opposition bloc is seeking to extend the probe for political reasons.

"The independent counsel should fulfill its duty within the time designated by the law," Rep. Chung Woo-taik, the floor leader of the Liberty Korea Party, said. "It cannot be extended indefinitely."

The special prosecutors' team formally launched a 70-day probe into the scandal involving the president and her friend Choi Soon-sil on Dec. 21.

Chung said the opposition bloc is only seeking to extend the probe to utilize it for the next presidential election, which may come earlier than December if the Constitutional Court approves the ouster of Park.

On Monday, the Liberty Korea Party announced that it will officially protest against the extension. (Yonhap)