President's security detail is South Korea's equivalent of US Secret Service

They made it past angry protesters and police barricades, but investigators trying to arrest the South Korean President on Jan 3 were thwarted by the impeached leader's security detail.

So who is still protecting Mr Yoon Suk Yeol and why? AFP takes a look at what we know:

WHAT HAPPENED?

Investigators from the Corruption Investigation Office issued a warrant to detain Mr Yoon for questioning over his Dec 3 declaration of martial law.

The judge specifically granted permission for them to enter a sensitive facility, as the presidential residence is classified.

But once inside, investigators said the Presidential Security Service (PSS) used minibuses and cars to block the driveway, then hundreds of PSS officers linked hands and formed a human chain to stop them.

Investigators pulled out, saying they feared for their safety.

"It is extremely worrying" because it was a stand-off between different branches of government, said Dr Vladimir Tikhonov, a Korean studies professor at the University of Oslo.

The showdown was "so far bloodless, but nobody guarantees that it will be continuously bloodless", he added.

WHAT IS THE PSS?