PHNOM PENH, Sept. 9 (FN) — Cambodia's Phnom Penh Municipal Court began trial of deputy opposition leader Kem Sokha on Friday for his "refusal to appear" in a prostitution case.

Security has been tightened at the court as dozens of opposition supporters rallied outside the court and a few hundred others gathered at the headquarters of opposition Cambodia National Rescue Party (CNRP) on the southern outskirts of Phnom Penh to protect Kem Sokha, who has holed up at the party's headquarters since May 26 for fear of arrest.

CNRP Vice President Kem Sokha was charged with "refusal to appear" in May after he ignored two court summons. Under the charge, he could face a prison term of between one and six months.

The accusation against Kem Sokha stems from leaked audio clips of telephone conversation between him and his alleged mistress in February. In the clips, they discussed sex, pregnancy and paying for an apartment.

Kem Sokha has not commented on the veracity of the audio recordings, instead advising his supporters not to respond to provocation.