It's the latest confrontation in a political crisis that has paralysed South Korean politics and seen two heads of state impeached in under a month.
South Korean authorities have entered the compound of impeached President Yoon Suk Yeol's official residence in Seoul to execute an arrest warrant over his short-lived imposition of martial law.
Investigators had to force their way through crowds of Yoon's supporters who had gathered outside the presidential complex and are now in a standoff with the Presidential Security Service (PSS).
The PSS previously blocked access to investigators with a warrant to search Yoon's office and residence and it is unclear whether they will try to prevent him being arrested.
It's the latest confrontation in a political crisis that has paralysed South Korean politics and seen two heads of state impeached in under a month.
It began on 3 December when Yoon, apparently frustrated that his policies were blocked by an opposition-dominated parliament, declared martial law and dispatched troops to surround the National Assembly.
Parliament overturned that declaration within hours in an unanimous vote and impeached Yoon on 14 December 14, while South Korean authorities opened a criminal investigation into the events.
Yoon has remained defiant, ignoring requests for questioning and vowing to fight to remain in office.
Four hours after dozens of investigators and police officers were seen entering the gate of the residence in Seoul to execute a warrant for Yoon’s detention, the dramatic scene appeared to have developed into a standoff.
The anti-corruption agency didn't immediately reply to questions about whether investigators successfully entered Yoon’s residential building, but South Korea's YTN television reported scuffles as investigators and police confronted the presidential security forces.
Seok Dong-hyeon, one of several lawyers on Yoon's legal team, confirmed that the investigators arrived at the building but said it was unlikely that they would be able to detain the president on Friday.
He said the agency's efforts to detain Yoon were "reckless" and showed an "outrageous disregard for law."
South Korea's Defence Ministry confirmed that the investigators and police officers got past a military unit guarding the residence's grounds before arriving at the building.
The presidential security service, which controls the residence itself, refused to comment on whether its members were confronting investigators and whether they planned to block the detention attempt.
The standoff prompted the liberal opposition Democratic Party to call on the country's acting leader, Deputy Prime Minister Choi Sang-mok, to order the presidential security service to stand down.
Choi, who also serves as finance minister, didn't immediately comment on the situation.
In a defiant New Year's message to conservative supporters rallying outside his residence, Yoon said he will "fight to the end" against "anti-state forces."
His lawyers have described the warrant as "invalid" and "illegal" and said that the presidential security force could arrest police trying to execute it.
Thousands of police officers gathered at Yoon's residence and formed a perimeter around a growing group of pro-Yoon protesters, who braved subfreezing temperatures for hours, waving South Korean and American flags while chanting slogans in his support.
There were no immediate reports of major clashes.
A Seoul court issued a warrant for Yoon's detention on Tuesday after he evaded multiple requests to appear for questioning and blocked searches of his office in Seoul, hindering an investigation into whether his ill-conceived power grab amounted to rebellion.
The warrant is valid for one week, and investigators may make another attempt to detain Yoon if they are unable to do so on Friday.