SEOUL: South Korean investigators called off their attempt to arrest impeached South Korean President Yoon Suk Yeol at his residence on Friday (Jan 3) over his failed martial law bid, citing safety concerns after a standoff with his security team.

"Regarding the execution of the arrest warrant today, it was determined that the execution was effectively impossible due to the ongoing standoff. Concern for the safety of personnel on-site led to the decision to halt the execution," the Corruption Investigation Office (CIO) said in a statement.

Authorities entered Yoon's compound earlier to execute an unprecedented arrest warrant, evading a crowd of protesters outside, but were confronted by presidential security forces inside.

Yoon, who has already been suspended from duty by lawmakers, would become the first sitting president in South Korean history to be arrested if the warrant is carried out.

The Presidential Security Service (PSS) has previously blocked access by investigators with a search warrant to Yoon's office and official residence.

Investigators from the CIO, including senior prosecutor Lee Dae-hwan, were let through heavy security barricades to enter the residence to attempt to execute their warrant to detain Yoon, AFP reporters saw.

But they were blocked by a military unit inside after entering, the Yonhap news agency reported. 

They later moved past that unit to confront security service members inside the residence.

Officials from the CIO, which is leading a joint team of investigators that includes the police and prosecutors, had arrived at the gates of Yoon's compound shortly after 7am (6am, Singapore time).

Media reports said the CIO vehicles did not immediately enter the compound, partly due to a bus blocking the driveway.

Some CIO officials later filed through an opened gate on foot and past the bus, but then briefly faced another bus and an armoured vehicle further up the driveway, before they were moved.

Soldiers under the Presidential Security Service at one point engaged "in confrontation with the CIO at the presidential residence", an official with Seoul's Joint Chiefs of Staff told AFP.

Yoon's security detail told AFP they were "in negotiation" with the CIO investigators, as they sought to access the president to execute their court-approved detention warrant.

Yoon's legal team – who raced to the residence and were allowed inside, AFP saw – decried the attempt to execute the arrest warrant.

Yoon's lawyer said in a statement on Friday that the execution of an invalid arrest warrant against Yoon was unlawful, and they would take legal action, without elaborating.

Two South Korean military officials, including army chief Park An-su who was named martial law commander during the short-lived declaration last month, have been indicted after being detained by prosecutors who are investigating insurrection charges, Yonhap reported on Friday.

Dozens of police buses and hundreds of uniformed police lined the street outside the compound in central Seoul, AFP reporters saw.

Some 2,700 police and 135 police buses have been deployed to the area to prevent clashes, Yonhap reported, after Yoon's supporters faced off with anti-Yoon demonstrators on Thursday.

Protesters gathered in the pre-dawn hours near the residence, with the numbers swelling into the hundreds amid media reports that investigating authorities would soon try to execute the arrest warrant that was approved on Tuesday.

"We have to block them with our lives," one was heard saying to others. About a dozen protesters tried to block a group of police officers at the entrance to a pedestrian overpass.

Some chanted "President Yoon Suk Yeol will be protected by the people", and called for the head of the CIO to be arrested.

Pyeong In-su, 74, said that the police had to be stopped by "patriotic citizens", a term Yoon used to describe those standing guard near his residence.

Holding a flag of the United States and South Korea with the words "Let’s go together" in English and Korean, Pyeong said he hoped incoming US President Donald Trump would come to Yoon's aid.

"I hope after Trump's inauguration he can use his influence to help our country get back on the right track," he said.

Jeremy Chan, a senior analyst at political risk consultancy Eurasia Group, said officials have resorted to arrest because of Yoon’s refusal to comply with investigators. He has thrice defied summons to appear for questioning. 

“The CIO has been tasked with investigating these valid insurrection charges against the president,” he told CNA’s Asia First.

“So, the fact that Yoon is taking this kind of absolutist, scorched earth approach is forcing the CIO to take more aggressive measures. Yoon is as guilty as any party in this whole drama in terms of escalating tensions and potential for violence.”

The current arrest warrant is viable until Jan 6 and gives investigators only 48 hours to hold Yoon after he is arrested. Investigators must then decide whether to request a detention warrant or release him.

Once arrested, Yoon is expected to be held at the Seoul Detention Center, Yonhap News Agency said, citing the CIO.

SURPRISE MARTIAL LAW

Yoon sent shockwaves through the country with a late-night announcement on Dec 3 that he was imposing martial law to overcome political deadlock and root out "anti-state forces".

Within hours, however, 190 lawmakers had defied the cordons of troops and police to vote against Yoon's order. About six hours after his initial decree, Yoon rescinded it.

He later issued a defiant defence of his decision, saying domestic political opponents are sympathetic to North Korea and citing uncorroborated claims of election tampering.

Kim Yong-hyun, who resigned as Yoon's defence minister after playing a major role in the martial law decree, has been detained and was indicted last week on charges of insurrection and abuse of power. 

Insurrection is one of the few criminal charges from which a South Korean president does not have immunity.

Yoon's lawyers have said the arrest warrant was illegal and invalid because the CIO did not have the authority under South Korean law to request a warrant.

Yoon has been isolated since he was impeached and suspended from power on Dec 14.

Yoon's legal team had already filed for an injunction to a constitutional court to block the warrant, calling the arrest order "an unlawful and invalid act", and also submitted an objection to the Seoul court that ordered it.

But the head of the CIO, Oh Dong-woon, has warned that anyone trying to block authorities from arresting Yoon could themselves face prosecution.

Along with the summons, a Seoul court issued a search warrant for his official residence and other locations, a CIO official told AFP.

Separate from the criminal investigation, his impeachment case is currently before the Constitutional Court to decide whether to reinstate or permanently remove him. A second hearing in that case is scheduled for later on Friday. 

Yongwook Ryu, an assistant professor at the National University of Singapore’s Lee Kuan Yew School of Public Policy, explained that there are grey areas under which Yoon could still be protected under presidential immunity.

He said officials should let the impeachment process run its course, rather than risk attempts to enforce Yoon’s arrest.

“I don’t quite understand why they want to push this through so urgently, when nothing much hinges on this particular arrest warrant,” he told CNA938.

“My expectation is that the Constitutional Court will uphold the impeachment. (When) he is no longer president, then the CIO, prosecutor's office, the police, all of them can investigate Yoon.”