South Korea authorities in standoff in bid to arrest impeached President Yoon Suk Yeol

Authorities entered impeached South Korean President Yoon Suk Yeol's compound on Friday to execute an unprecedented arrest warrant, evading a crowd of protesters outside, but were confronted by presidential security forces inside.

It was unclear whether the Presidential Security Service (PSS), which has previously blocked access by investigators with a search warrant to Yoon's office and official residence, would try to stop him from being arrested.

Yoon is under criminal investigation for insurrection over his December 3 martial law attempt that stunned South Korea, Asia's fourth-largest economy and one of the region's most vibrant democracies.

An arrest would be the first for an incumbent South Korean president.

Officials from the Corruption Investigation Office for High-ranking Officials (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 7 am (2200 GMT Thursday), according to Reuters witnesses.

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.

Cordons

Once inside the compound, the CIO and accompanying police faced cordons of PSS personnel, as well as military troops seconded to presidential security, media reported. South Korea's Ministry of National Defence said the troops were under the control of the PSS.

Yonhap news agency cited the head of the PSS saying the authorities are not allowed to search Yoon's residence.

As of 1 pm, the standoff continued.

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

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 after Yoon refused summons to appear.

"We have to block them with our lives," one was heard saying to others.

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, 71, 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.

The current arrest warrant is viable until January 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 Centre, Yonhap News Agency said, citing the CIO.

Martial law shocker

Yoon sent shockwaves through the country with a late-night announcement on December 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.

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.

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.

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.