A 21-year-old man was hauled to jail on suspicion of posing as a cop during a violent robbery in Parkmerced on Wednesday morning, San Francisco police said.

After claiming he was an officer, the suspect chased down and beat up a 19-year-old man in the 300 block of Font Boulevard just after 3 a.m., police said.

The thug demanded money before ripping a necklace off the victim’s neck. The victim suffered a cut to his elbow and complained of pain to his mouth, but his injuries were not serious, police said.

Officers later arrested the suspect, but did not recover the necklace.

maldax@sfexaminer.com