A PKR supporter who slapped party vice-president Chua Tian Chang yesterday has been detained, said police.
The 32-year-old man is said to be a member of Gombak PKR division and was detained after the incident.
The case is being investigated under Section 147 of the Penal Code for rioting.
The police said more arrests are expected.
Earlier, Chua, who is popularly known as Tian Chua, was surrounded and attacked by a rowdy group outside the PKR headquarters over his links with sacked deputy president Azmin Ali.
Meanwhile, PKR president Anwar Ibrahim said he will not compromise with violent supporters.
“I have no choice but to leave the matter with the authorities as well as the party’s disciplinary board to take action.
“A hardcore supporter must be disciplined and refrain from verbally abusing others and slandering people,” he said.