South Korean President Yoon Suk Yeol vowed on Saturday to fight for his political future after he was impeached in a second vote by the opposition-led parliament over his short-lived attempt to impose martial law, a move that had shocked the nation.

The Constitutional Court will decide whether to remove Yoon sometime in the next six months. If he is removed from office, a snap election will be called.

Prime Minister Han Duck-soo, who was appointed by Yoon, became acting president while Yoon remains in office but with his presidential powers suspended halfway through his five-year term.

"I will give all my strength and efforts to stabilise the government," Han told reporters after the vote.

Later, he chaired a National Security Council meeting and urged the country to maintain a "watertight readiness posture" to ensure North Korea could not plan any provocations. The political crisis, which has led to the resignation or arrest of several senior defence and military officials, has raised concerns over the South's ability to deter nuclear-armed North Korea at a time when Pyongyang is expanding its arsenal and deepening ties with Russia.

Yoon is the second conservative president in a row to be impeached in South Korea. Park Geun-hye was removed from office in 2017. Yoon survived a first impeachment vote last weekend, when his party largely boycotted the vote, depriving parliament of a quorum.