Malaysia's Prime Minister Abdullah Ahmad Badawi vowed Friday to suppress a weekend political rally, backing police who warned they will break up the protest and arrest participants.

New York-based Human Rights Watch slammed the government's stance on the mass rally planned for Saturday, which organisers hope will attract tens of thousands of people, saying it made a mockery of Abdullah's reform ambitions.

The premier was adamant as he closed his ruling party's annual talks, saying he was trying to avoid violence breaking out at the protest, which the three main opposition parties and civil society groups are taking part in to campaign for clean elections.

"If there is a clash, people will not be happy. This is something that we are trying to avoid," he told reporters.

"Police have not issued a permit for the rally to take place tomorrow. So it will not take place tomorrow."

Police chief Musa Hassan told the state Bernama news agency that there was a risk of rioting and property destruction at the event in Kuala Lumpur's Independence Square.

"Members of the public found in the area to attend the gathering are committing an offence and legal action will be taken against them," he said, adding that 4,000 police would be on duty and roadblocks set up around the venue.

Human Rights Watch called on the government to support free speech as it heads towards elections expected to be called early next year.

"The grounds for refusing the rally are nonsense," said its Asia director Brad Adams.

"If Malaysia wants to count itself a democracy, it can begin by upholding constitutional guarantees of free speech and assembly. The way the system works now, only the ruling coalition can get its messages out."

Human Rights Watch said Malaysian elections have been sullied by vote-buying, the use of public resources by the ruling parties and accusations of bias against the Election Commission.

"The government should not be afraid to allow Malaysians to raise very basic issues about the fundamental right to vote," Adams said.

Former deputy premier Anwar Ibrahim, who was heir apparent to former premier Mahathir Mohamad until his sacking in 1998 when he was jailed for six years for sodomy and corruption, is to address the rally.

Anwar's sodomy conviction was later overturned but the corruption verdict stands, barring him from standing for public office until April 2008.

Protests are rare in Malaysia, and the last major rallies were seen in 1998 during the "Reformasi" or "Reform" movement which erupted after Anwar's sacking. They were suppressed by police with water cannons and mass arrests.

Abdullah condemned the opposition alliance organising the protest as an "illegal group" and said it was the wrong way to push for change.

"They show no concern for the law and no respect. I am sad. Why are they doing this to challenge the government?"