South Korea's electoral body voiced concern on Saturday over heightened tensions between supporters and opponents of ousted president Park Geun-hye, a day after violent police clashes left three people dead and dozens wounded.

The Constitutional Court decision on Friday to uphold a parliamentary vote to impeach Park over a corruption scandal prompted her angry conservative supporters to take to the streets of Seoul. Two people were killed in protests with riot police, while a third elderly man had a heart attack and died on Saturday.

The opposition has been gathering for weeks calling for her ouster and now demands she now face criminal charges and arrest.

Police on Saturday braced for more large-scale protests from both sides, raising the risk of more violent clashes.

The head of the National Election Commission, Kim Yong-deok, said in a televised address that he was concerned over an "overheated" environment and asked the public to avoid "conflict." He said snap elections would be free and fair and held by May 9.

"The vote must serve as a chance to overcome divisions and conflicts and achieve national unity and harmony," Kim said.

Liberal candidate, Moon Jae-in, is leading the opinion polls.  

Park's dramatic downfall followed months of political instability over a corruption scandal that has also led to the arrest of the head of the Samsung conglomerate. Park was accused of bribery and abuse of power by allegedly conspiring with her friend, Choi Soon-sil, a private citizen, to extort money from businesses.

Choi, Samsung heir Lee Jae-yong and other top officials have been arrested over the allegations.

Park has not made a statement and remained holed up in the presidential palace, but would soon leave to her private residence, a spokesperson said.

The court verdict strips Park of immunity, raising the prospect of her arrest and prosecution.

cw/rc (AFP, AP, Reuters)