Protesters stage a rally calling for impeachment of South Korean President Park Geun-hye as the Constitutional Court holds its final hearing in the impeachment trial of Park in front of the court in Seoul in Seoul, South Korea, Monday, Feb. 27, 2017. A special investigation team is wrapping up its probe into a huge scandal involving Park after the country's acting leader refused to extend its investigation past a Tuesday deadline. The sign read: "Impeach Park Geun-hye immediately." (AP Photo/Ahn Young-joon)

SEOUL, Korea, Republic Of - South Korea's main opposition parties threatened Monday to impeach the country's acting leader after he refused to extend a special investigation into the huge corruption scandal that toppled conservative President Park Geun-hye.

If successful, the impeachment of Prime Minister Hwang Kyo-ahn would rile an already tumultuous political landscape, putting another interim leader in power while the constitutional Court decides the fate of both Hwang and Park, who's now on trial.

On Monday, Hwang refused a request by the investigation team to extend its probe past Tuesday's deadline. A spokesman for Hwang said the team led by independent counsel Park Young-soo has already indicted key figures implicated in the scandal and that state prosecutors can look into any other areas.

Prosecutors say President Park allowed her confidante to meddle in state affairs and that they colluded to extort money from companies.

The three main liberal opposition parties spearheaded Park's December impeachment and vowed immediately to push for Hwang's.

His decision shows he's trying "to become Park's shield to protect her and her associates," said Choo Mi-ae, leader of the main opposition Democratic Party.

Impeaching a prime minister requires support from half of the 299-member parliament. The three parties have a total of 166 seats, meaning they can easily reach the threshold to strip Hwang of power. But critics say the opposition parties must also consider the possibility of a strong backlash from conservatives if they make another high-profile impeachment effort.

Monday was also the final day of arguments at the constitutional Court, which is deliberating on whether to formally end Park's rule or restore her presidential powers. It's not clear when there will be a decision. If Park is ousted for good, a presidential election must take place within two months of the ouster to choose her successor.

Hwang is considered a potential conservative contender for president if that byelection occurred. In an opinion poll released Monday, Hwang ranked third behind two liberal opposition politicians.

Lee Kyu-chul, a spokesman for the investigation team, described Hwang's decision to reject the extension of investigation as regrettable.

Weeks of rallies by huge crowds angered by the scandal forced Park to offer a public apology and approve the independent counsel investigation days before her impeachment.

The team has since arrested former top Park administration officials and other high-profile figures such as Samsung heir Lee Jae-yong. Park, who denies the allegations, has avoided a direct investigation because of a law that gives a sitting leader immunity from prosecution.

News from © The Associated Press, 2017