S Korea court begins review of president's impeachment

South Korea's Constitutional Court has begun reviewing the impeachment of President Yoon Suk Yeol over his martial law attempt, starting a process to decide if he will be removed from office, while investigators plan to question him this week.

The court will hold the first public hearing on December 27, spokesperson Lee Jean told a news conference, after the court's six justices met to discuss plans for reviewing the impeachment by the opposition-controlled parliament on Saturday.

The court has up to six months to decide whether to remove Yoon from office or to reinstate him. The first hearing will be "preparatory" to confirm major legal issues of the case and schedule among other matters, Lee said.

Yoon is not required to attend that hearing, he said.

In 2017, the court took three months to issue a ruling to strip then-President Park Geun-hye's presidency following her impeachment for abusing the powers of her office.

Yoon and a number of senior officials face potential charges of insurrection, for the short-lived martial law.

A joint team of investigators from the police, the defence ministry and an anti-corruption agency are planning to call Yoon in for questioning on Wednesday, a police official told Reuters.

Investigators tried to serve a summon for Yoon to appear by delivering it to the presidential office and his official residence, but the presidential security service declined to receive it saying it was not in the position to do so, Yonhap news said.

On Sunday Yoon did not appear in response to a summons for questioning by a separate investigation by the prosecutors' office, Yonhap news reported. Yoon cited he was still forming a legal team for his defence as the reason, it said.

The government led by acting president, Han Duck-soo, was moving quickly to reassure international partners and calm financial markets, while the main opposition party pledged to co-operate in efforts to stabilise the situation.

Yoon's surprise martial law declaration and the ensuing political crisis spooked markets and South Korea's diplomatic partners, worried over the country's ability to deter nuclear-armed North Korea.

In one of his first moves as acting president, Han spoke with US President Joe Biden by telephone on Sunday, pledging unwavering commitment to pursue foreign and security policies based on the alliance between the two countries.

Opposition Democratic Party leader Lee Jae-myung welcomed US President-elect Donald Trump's selection of his former intelligence chief to handle special missions including North Korea as a sign of commitment for dialogue to ease tensions.

Foreign Minister Cho Tae-yul said the nomination of Richard Grenell indicated North Korea will be one of the top priorities of Trump's presidency. Trump met North Korean leader Kim Jong Un on three occasions during his first term.

The benchmark KOSPI index fell on Monday, after last week's sharp gains prior to the impeachment, as traders were seen booking profit amid eased political uncertainty.

The Saturday impeachment vote passed with at least 12 members of Yoon's ruling People Power Party joining in favour, which has thrown the party into a disarray with its leader Han Dong-hoon announcing his resignation on Monday.

- with AP