Malaysian police are warning activists not to participate in an upcoming rally in support of opposition leader Anwar Ibrahim.

Opposition activists are calling for a large protest in front of the Kuala Lumpur High Court on Monday, where a judge is expected to deliver a verdict in Anwar's nearly two-year-long sodomy trial.

But Kuala Lumpur Police Chief Mohmad Sallel said late Monday that “stern action” will be taken against anyone participating in the protest. He says the gathering is illegal and would do “untold harm to the public.”

Anwar faces up to 20 years in prison if convicted on charges of sodomizing a former political aide.

The former deputy prime minister has repeatedly said he is innocent and that the charges are politically motivated by his rival, Prime Minister Najib Razak.

Mr. Najib has denied this claim.

The allegations against Anwar emerged months after his party made major gains in Malaysia's last parliamentary elections. A conviction would prevent the 64-year-old politician from running in national elections expected next year.

Anwar was forced to step down as deputy prime minister in 1998 after being convicted of sodomy. The Supreme Court overturned the conviction and he was released in 2004. Sodomy is illegal in Muslim-majority Malaysia.

Rights groups have criticized Malaysia's government for cracking down against and strictly regulating public protests. In the past, Malaysian authorities have disrupted street protests by making mass arrests and using roadblocks, tear gas and water cannons.