By Hyunjoo Jin and Hyonhee Shin

Seoul (Reuters) - South Korean President Yoon Suk Yeol's security chief said on Friday the impeached leader, who faces arrest over a criminal probe into his Dec. 3 martial law bid, has been unfairly treated for a sitting leader and warned bloodshed must be avoided.

Park Chong-jun, head of the Presidential Security Service (PSS), is himself under investigation for obstructing official duty related to a six-hour standoff last week between PSS agents and investigators trying to execute an arrest warrant for Yoon.

Arriving at police headquarters for questioning, Park, who is a former senior police official, said the current attempt to arrest a sitting president is wrong and Yoon deserved treatment "becoming of" the country's status.

"I believe there should not be any physical clash or bloodshed under any circumstances," Park told reporters, adding acting President Choi Sang-mok has not responded to his request for safety assurances for officials involved.

Hundreds of PSS agents blockaded the presidential compound and thwarted investigators from trying to arrest Yoon. The investigators were pulled back because of the risk of a clash.

Officials of the Corruption Investigation Office for High-ranking Officials (CIO), which is leading the investigation, have said PSS agents were carrying firearms during the standoff although no weapons were drawn.

The investigators obtained a new arrest warrant this week after the embattled leader defied repeated summons to appear for questioning.

On Thursday, lawyers for Yoon said the arrest warrant was illegal and invalid.

Yoon is under a separate Constitutional Court trial reviewing parliament's impeachment of the suspended leader on Dec. 14 to decide whether to remove him from office permanently or reinstate him.

(Reporting by Hyunjoo Jin and Hyonhee Shin; Writing by Jack Kim, Editing by John Geddie, Ed Davies)