SEOUL - South Korean police started on Tuesday providing additional security for the leader of the main opposition Democratic Party, after lawmakers had warned of a potential assassination plot targeting Lee Jae-myung, the Yonhap News Agency reported.

The move comes after the party had last week urged police to ramp up security for Lee after some of its lawmakers said they were tipped off about an assassination plot against him.

Police did not immediately respond to a request for comment.

In January last year, Lee was stabbed in the neck by a man who lunged at him with a knife after asking for his autograph.

The man was sentenced to 15 years in prison, according to media reports.

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Tensions have been running high in South Korea since President Yoon Suk-yeol briefly imposed martial law last December, triggering the country's worst political crisis in decades.

His martial law imposition and its fallout have widened deep social rifts between conservatives and liberals and put pressure on institutions.

Yoon faces a criminal trial on charges of insurrection, while the Constitutional Court is also expected to rule in coming days on whether to uphold his impeachment and permanently strip him of his powers.

Police have been preparing for the risk of clashes, with both Yoon's supporters and his opponents are due to hold large rallies when the court makes its decision.

South Korea's Acting President Choi Sang-mok repeated on Tuesday a call for citizens to accept and respect the court's ruling.

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Hundreds of Yoon supporters stormed a court building in January after his detention was extended, smashing windows and other items, an attack the acting leader called "unimaginable".